GB2270395A

GB2270395A - Water purification system

Info

Publication number: GB2270395A
Application number: GB9318064A
Authority: GB
Inventors: Brian Michael Morris
Original assignee: Honeywell Control Systems Ltd
Current assignee: Honeywell Control Systems Ltd
Priority date: 1992-09-02
Filing date: 1993-09-01
Publication date: 1994-03-09
Anticipated expiration: 2013-09-01
Also published as: GB9318064D0; GB2270395B

Abstract

A cooling-tower water re-circulating system 1 for maintaining water cool for use in an air-conditioning system 2 has a purification unit incorporating a silver and copper ion generator 17 whose ion output is controlled by control unit 12 in accordance with the measured ion content in the water determined by ion sensors 14, 15 and 16 and also with other operations of the system such as draining the system when the detected impurity level exceeds a threshold. In this way, efficient and effective purification with continual monitoring is achieved. The ion sensors 14, 15, 16 each comprise an elongate body of material including platinum which is immersed in the water to be tested whereby the ion content of the water is derived from the charge detected in the body. <IMAGE>

Description

WATER PURIFICATION SYSTEM The present invention relates to apparatus for, and a method of, purifying water.

It is well-known that silver ions are very effective in killing many types of bacteria occurring in water, and there exist numerous arrangements of water recirculatory systems in which electrolyticly generated silver ions are used to maintain the water clean.

If the generator is under-driven (i.e. the driving current input to it is frequently below an adequate value), then the cidal affect on the bacteria in the water will become ineffective allowing build-up of bacteria to happen, whether temporarily or continuously. In order to avoid this possibility, the generator tends to be over-driven rather than under-driven.

However, over-driving also causes problems in that it tends to cause the electrodes to wear out quickly, thereby increasing the cost of materials and adding to the maintenance and checking required, all this causing an increase in the operating costs. Also the possibility of build-up of harmful and potentially explosive gases is increased.

In some purification systems some form of control has been achieved by monitoring fluctuations in the current level being input to the generator and making appropriate adjustment^. However, such an arrangement is very susceptible to various inaccuracies including water hardness, impurities in the water, the occurrence of scaling and the possibility of shorting between the electrodes.

International patent specification number JO 85/00034 describes a water purification system with a silver ion generator in which it is supplied with electrical power taken from the circuit to the pump, thereby ensuring that the generator operates only when water is circulating. The generator includes circuitry to maintain a stable current between the electrodes throughout generation of the silver ions, but this does not mean that the level is at an optimum for any circumstances.

US Patent Specification 5114571 describes a water treatment system having an electrical conductivity detector which measures the amount of salts in the water in order to monitor the levels of total dissolved solids (TD8) and, if a predetermined set point is reached, to start the blow-down operation. US Patent Specification 5114571 discloses that if the ion content sensed is greater or less than the set point, power for the silver and copper ionizing devices is increased or decreased as required, there being no disclosure of how the ion content is sensed.

According to the invention, a water purification system comprises means to input silver ions into water; means to measure the amount of free ions in the water; means to vary the silver ion input in dependence on the output from the ion measurement means.

In this way, the invention provides that the generation of silver ions is effected according to the amount of free ions in the water and not in accordance with the amount of salts in the water measured by the electrical conductivity of the water, as might be done in US Patent Specification No 5114571. Thus the invention can ensure that the input of ions into the water is at a level which is adequate to maintain effective killing of the bacteria in the water without undue cost or detrimental effects.

Preferably, the ion measurement means comprises means to measure any change in the amount of free ions in the water. In this way, the invention can provide continuously varying control of the silver ion generation process thereby ensuring that the correct silver ion levels in the water are precisely and quickly achieved. This differs from US Patent Specification 5114571 in which there is only sensing as to whether a set point is exceeded or not met.

Moreover, this allows the level of change of silver ions generated to vary in accordance with the change in amount of ions measured. US Patent Specification 5114571 merely states that power for the ionizing devices can be decreased or increased if the sensing indicates that the set-point is exceeded or not met, there being no suggestion that there is any variation in increase or decrease of the power levels.

The system may have means to monitor the ion content in the water for any change in ion control correlated to a change in the silver ion generation; this may be used in modifying operation of the silver ion generation to ensure that the correct amount is achieved precisely and quickly, thereby minimising the possibility of overshoot and wastage.

Advantageously, the ions input means comprises means to generate ions electrolyticly. Moreover, preferably, there is provided a chamber through which water flows, said ions input means being operable to input the ions into water as it flows through said chamber.

Measurement of the ion content and/or any change of the ion content may be effected upstream of the input of the ions, or it may be effected both upstream and downstream.

In the latter case, the ions input means is operable to input ions into water at a rate in dependence on measurement of, for example, the difference between ions measured in the water upstream and downstream of the input of the ions.

Preferably, the water purification system has means to measure the amount of ions and/or any change of the ion content in the water, said measurement means having a body of material containing platinum, which body is for exposure to a flow of water for which the ion content and/or any change of the ion content is to be measured, means to detect electrical charge in said body and means to derive, from the detection means, a value for the ion content and/or any change of the ion content in the water. The body of material may be substantially pure platinum, and it may be in an elongate or a plate form, and it may be substantially enclosed in an electrically insulated material other than that part which is for exposure to the flow of water.

The charge detection means may include means to amplify and/or to measure any electrical voltage detected.

The invention is applicable to copper ions which inhibit algae growth and to other similar and appropriate ions.

The invention also provides a method of purifying water comprising inputting silver ions into water at a rate in dependence in the amount of free ions, and/or any change in the amount of ions, measured in the water.

Thus in the invention, a method of purifying water comprises inputting silver ions into water; measuring the amount of free ions in the water; varying the silver ion input in dependence of the measurement of ions in the water.

Preferably, the ion measurement stage comprises means to measure any change in the amount of free ions in the water.

Preferably, the method comprises measuring the ion content, and/or any change in the ion content, upstream of the input of the ions, or measuring the ion content upstream and downstream. In the latter situation, the ion input is varied in dependence on measurement of, for example the difference between, ions in the water upstream and downstream of the input of the ions.

Other significent benefits of the invention are that it enables the frequency of service calls to the system by engineers to be significently reduced and it eliminates inherent measurement errors that exist in prior art systems.

For example a prior art system typically needs to be checked every week in order to determine, by chemical analysis, whether the rate of ion generation is adequate or excessive; the engineer uses the result of that single test (which only indicates the situation at that particular time) to decide whether, and what, manual adjustment of the ion generator controls is required. His decision can only be verified (or otherwise) by the results of his chemical analysis in the next call a week later, and either or both results could be highly misleading in that they could represent an instantaneous amount of a variable rather than a steady state value.Thus, with such a testing and servicing arrangement, it is quite possible that between tests the ion content in the system fluctuates significently on either or both sides of the optimum levels, thereby risking the proliferation of bacteria and/or reducing the efficiency of operation of the system.

In a system embodying the present invention, the engineer need only make a service call once a month at most and when he does, then, in respect of the ion generator, it is only in order to check the electronic components and circuitry, no chemical analysis or manual adjustment being necessary. Clearly the present invention also eliminates those inaccuracies inherent in the test results in the prior art systems.

According to another aspect of the invention, there is provided apparatus for the measurement of free ions, and/or any change in the amount of free ions, in a fluid stream, the apparatus comprising a body of material containing platinum, which body is for exposure to a stream of fluid for which the free ion content, and/or any change in the free ion content, is to be measured, means to detect electrical charge in said body and means to derive, from the output of the detection means, a value for the free ion content, and/or any change in the free ion content, in the fluid.

Such apparatus can provide measurement of the free electrical ions in the water, whereas conductivity detectors of the prior art measure the amount of salts in the water.

Thus, this can provide an improved measurement of ion content, and/or any change in ion content, in the water.

Such apparatus is simple in construction and low-cost compared to prior art conductivity probes or detectors involving membranes. Moreover such apparatus has very little effect on the flow characteristics of the water under test.

This aspect of the present invention also provides a method of measuring the ion content, and/or any change in the ion content, in a fluid stream, the method comprising exposing a body of material containing platinum to a stream of fluid for which the ion content, and/or any change in the ion content, is to be measured, detecting electrical charge in said body and deriving, from the results of the detection stage, a value for the ion content, and/or any change in the ion content, of the fluid.

The water purification system, and the method of purifying, is applicable to a wide variety of situations, for example air-conditioning systems, swimming pools, hotwater or downwater systems whether for domestic, commercial or industrial buildings.

The apparatus for ion measurement, and the method for measuring ions, is applicable to a wide variety of situations including but not limited to water purification systems. It can be used in relation to silver ions, copper ions or other ions.

In a further application, the present invention may be used for the control of bacteria in a body of liquid, for example water-based liquid, which body is stored and/or circulated for use in industrial manufacture, for example in a cleaning process, or a heating/cooling process or a lubricating process, or a sharpening process. Thus for example the invention may be used to control bacteria in a cutting fluid reservoir used in blade sharpening or honing processes for industrial cutter machines in a factory.

Another aspect of the present invention provides a water re-circulating system comprising reservoir means to hold water, means to detect the amount of dissolved solids in water held in the reservoir means, valve means to effect draining of water from the reservoir means and control means to control flow through the valve means in accordance with the output from the detection means.

A further aspect of the present invention provides a water re-circulating system in which a number of operations are performed on water in the system, the system comprising means to effect cooling of water in the system, means to drain water from reservoir means to hold water in the system, means to generate silver ions for input into the water, and microprocessor control means to monitor and effect control of said cooling means, said drain means and said ion generating means.

In order that the invention may more readily be understood, a description is now given, by way of example only, reference being made to the accompanying drawings in which : Figure 1 is a block schematic diagram of a water recirculating system embodying the present invention; Figure 2 is a block schematic drawing of a ion sensor of Figure 1; Figure 3 is a block circuit diagram of the ion sensors control circuit; Figure 4 is a block schematic diagram of a domestic downwater system embodying the present invention; and Figure 5 is a block schematic diagram of a sealed cooling tower embodying the present invention.

Figure 1 indicates schematically a water re-circulating system generally designated as 1 which maintains and cleans the water used in an air-conditioning system 2 in a large office building. Water output from the air-conditioning system 2 passes through a series of sprays 3 into a cooling tower 4 where it is subjected to streams of air urged upwardly by fans 5 to cause evaporative cooling and then is held in a reservoir 6 of the cooling tower. Water is taken out of the reservoir 6 and returned to the air-conditioning system 2 as required.

Water in the system 1 is maintained clean by a water purification unit 7 which has a by-pass water circuit 8 extracting a proportion of the water from system 1 by means of regulating valve 9 having only two working positions ("fully open" and "fully closed"), adding at a chamber 10 ions supplied from an ion generator 11 and then returning the water to the system 1. The amount of water which is extracted in this way, and the amount of ions input into the water, is controlled from a microprocessor-driven main control unit 12 by varying the relative time durations for "open" and "closed" settings of valve 9.Also, control unit 12 can receive data inputs from a water meter 13 which measures the water flow input in system 1 and from ion sensors 14, 15 and 16 which are located, respectively, in the pipework of system 1, adjacent to the inlet for chamber 10 and adjacent to the outlet to chamber 10. By suitable processing of all this data, control unit 12 is able to ensure that the current applied to silver electrode 17, which together with the electrically earthed walls of chamber 10 constitute the ion generator 11, is maintained at all times at the minimum level necessary to ensure that the silver ion content in the water is adequate to kill bacteria throughout system 1.

The water purification unit 7 may have a number of the chambers 10 arranged in parallel in order to increase the amount of water which can be treated at a given time, a typical flow rate through one chamber being 0.25 litres per second. Each chamber may have a separate ion sensor at its inlet and/or outlet, or some or all chambers may share ion sensors, as deemed appropriate.

Normally, electrode 17 includes some copper as well as silver (of known proportion so that the respective generation rates of silver and copper ions is determinable by control unit 12), so that copper ions are generated as well as silver ions, as copper ions are known to inhibit algae growth.

Alternatively, the copper ions can be generated in separate chambers which may be in series or in parallel with the silver ion chambers and may be structurally the same except for incorporating a copper electrode rather than a silver electrode. The rate of generation of copper ions from a chamber may be controlled in the same manner as with the silver ions and incorporating either the same mathematical relationship between ions measured and generated or an appropriate different such relationship.

Generally, any aspect described herein concerning the generation of silver ions is applicable also to the generation of copper or other similar and appropriate ions.

In Figure 1, a data link between any given component (eg. sensor 14) and control unit 12 is shown by a broken line extending horizontally away from the component and with the principal direction(s) of communication being represented by one or more arrows.

When the water level in system 1 needs to be topped up, water is passed from the mains into the water reservoir 6 via inlet valve 42.

Figure 2 shows a cross-sectional view of ion sensor 14 located in the sidewall 20 of the purification system 7, the sensor having a platinum probe 21 of diameter 0.5 mm and length 5.0 mm, one end of probe 21 being electrically connected to a stainless steel terminal 22, the opposite end being positioned within the duct and exposed to the water flow while the remainder of probe 21 is enclosed in electrically insulating epoxy material 23. In operation, flow of water containing silver ions causes a flow of charge within probe 21 which can be picked up via terminal 22 and electrical leads 24 and, after appropriate signal conditioning eg buffering, filtering and/or off-setting as required, it can then be used as an input data signal for control unit 12.

Thus, in Figure 3, the flow of silver ions in the water passing ion sensors 14, 15 and 16 causes an accumulation of charge at the respective sensors which can be detected by voltage detectors 30. As the voltages are typically of the order of a few mV, they are amplified at amplifiers 31 before input, via communication bus 32, to the interface unit 33 of control unit 12 which also receives in similar fashion data input from the water meter 13 and the sensors and components of the other operations and routines which are described below.

All this data is input to processor unit 34 of control unit 12 which continually monitors all operation variables, especially the instantaneous ion-content, change in ioncontent and water flow values in the system, in order to ensure economic driving of electrode 17 and operation of valve 9; other operation variables which are monitored include fans 5 and the draining routine. To this end processor unit 34 continually uses, and up-dates, data held in store 35 which includes both generic operating data of typical systems and also historic data on the operation of this particular installation.Use of the data in store 35 provides an efficient start-up having an early cidal effect on bacteria when the installation is being first commissioned or re-commissioned, as well as economic yet effective control of silver ion generation during the dosing and other routines of the installation for example as described below. When control unit 12 notes any change in ion content, it alters the ion generation to a level in accordance with that change, this process being continual, enabling variations in the changed levels of silver ionisation and ensuring that the correct level of silver ion content is achieved precisely and quickly.The control unit can also monitor ion content changes to correlate them with silver ion generation changes in order to further improve the efficiency and efficacy of the silver ion generation operation, and in order to refine measurement of the silver and other ions content.

Control unit 12 also monitors all the operations and routines for malfunctions of the components and systems so that, upon detection of a fault or other alarm condition (e.g. leakage in the water-recirculating system or low stocks of chemicals) it can alert a remote alarm unit 36 and a display terminal 37 which are linked to communication bus 32 and which are in a locality where they are regularly viewed, eg. by the buildings caretaker or by the systems maintenance company. Remote alarm unit 36 and display terminal 37 may be located in a central operations room from which a maintenance company can monitor a number of separate water re-circulating systems.Control unit 12 can send details of the nature and location of the fault for display at terminal 37, and can receive back instructions and/or additional data (whether keyed in by an operator or sent automatically according to predetermined instructions) from terminal 37 which may be linked to bus 32 by public or private telephone network or by a dedicated link.

Control unit 12 also monitors for the build-up of disolved solids within the water in the system especially reservoir 6, and/or the pipework of the system using data received via communication bus 32 from at least one meter 40 located in reservoir 6 and/or the pipework of the system to give a total dissolved solids" reading by measuring the relative electrical conductivity of the water. When control unit 12 determines that a critical value has been reached (for example 3000 5), it instructs regulating valve 41 to open in order to drain water and associated solids from the reservoir 6, the reduction in water level causing ball-cock valve 42 to open and hence replenish, from a mains water supply, water in the reservoir to the normal level; alternatively, control unit 12 may directly control the rate/amount of replenishment water.When a number of meters 40 are located throughout the reservoir and the pipework, control unit 12 makes use of a different threshold value for each meter, appropriate to its position in the system; moreover, control unit 12 can use each threshold in isolation, or it can take account of the measured values from, and the threshold values of, one or more other meters.

Regulating valve 41 has only two working positions, fully open and "fully closed, but control unit 12 can control the relative time duration in each position in order to modulate the amount of water flowing in a given time period. Thus throughout the drain routine, control unit 12 checks the instantaneous output of the meter(s) 40 and, after considering data from store 35 and other input data, it determines whether it is appropriate for valve 41 to remain continually open or whether, because the drain operation is entering a later phase, the valve 41 needs to be controlled in an intermittent open/closed manner in order to reduce the water flow in a given time period.Clearly, as the measured values from meter(s) 40 approaches the required amounts, control unit 12 changes the open/closed ratio to further reduce the amount of water which flows in a given time. In this way, there is no "over-shoot" of the control in the drain routine which would cause excessive draining of water and hence additional use of ions and dosing chemicals to bring the water of the system up to the required levels; nor is there @undershoot@@ of the drain operation which would hazard an early repeat of the drain procedure. This control of valve 41 by control unit 12 ensures that this precise draining of the necessary amount is achieved without necessitating an expensive modulating valve.

During or at the end of a drain routine, control unit 12 makes appropriate adjustments to the ion generation and any chemical dosing operations in order to ensure continued safe and economic purification and supply of water to airconditioning system 2.

In operation of the drain routine, control unit 12 can vary the critical level of solids build-up and/or the start of the drain routine according to circumstances and/or the other operations and routines of the water re-circulating system 1, and so modify appropriately the flow rate, and length of time, of drain.

Thus the provision of a control unit to operate a simple, low-cost "on/off" regulating valve 41 provides substantially increased flexibility and control in the drain routine, together with more precise and less wasteful draining ensuring less containment water being discharged to drain.

Another function of control unit 12 is to operate and monitor the dosing operations for the corrosion-prevention chemicals and for any biocidal chemicals which may be required, especially for example during initial commissioning of the installation when, for a period, the amount of silver ions accumulated throughout the water recirculating system 1 may be inadequate to ensure a thorough cidal effect on bacteria.

Thus, at least one detector 50 of corrosion-prevention chemicals and at least one biocide detector 51 are located in reservoir 6 thereby providing control unit 12 with continuous data on chemical levels in the water.

When deemed appropriate by control unit 12 (either by virtue of measured values or of the occurrence of other routines of the system), it instructs operation of a pump 53 to supply chemical from a storage tank 54 of corrosionprevention chemical, or from storage tanks 55 or 56 of two different biocides which are used alternately in order to inhibit the build-up of bacteria resistant to a given biocide. Control unit 12 records the amount of use of chemicals from tanks 54 to 56 in order to note when the stocks are becoming low and require replenishment. Each tank may also have a level detector to advise the control unit 12 when a given level is reached.

In regulating the dosing operation, control unit 12 notes the amount of replenishment water as measured by meter 13, thereby taking account of any loss of water caused by the drain routine, or by topping-up in the ion generation operation, together with any evaporation losses caused during the cooling operation when control unit 12 is operating sprays 3 and fans 5.

Accordingly, control unit 12 is able to add the chemicals as the water in reservoir 6 is being replenished, ensuring that there are no temporary drops below safe or effective levels, while ensuring minimal amounts of the chemical are actually used, this being particularly important as these chemicals are expensive, toxic and extremely unpleasant to handle. 8paring use of the chemicals also reduces the frequency with which the tanks need to be re-filled.

Store 35 of control unit 12 holds data on water changes and dosing produced by operations in generic water recirculating systems and historically in system 1, so that control unit 12 can use such data during the regulation of the dosing operation.

A meter 57 to measure bacteria levels is located in the reservoir 6 and/or elsewhere in water re-circulating system 1 in order to pass any data on the build-up of general or specific bacteria to control unit 12 which can then take appropriate action in relation to ion generation and any other operation as required.

Control unit 12 monitors, and controls, the operation of a filtration unit 58 and diverter valve 59 to get rid of solids and particles in the water before return to airconditioning system 2.

Thus control unit 12 continually monitors the entire system and effects, controls and adjusts all the operations when the need arises rather than, in the prior art, some of the operations only being effected or adjusted during a service visit. In considering whether a given operation is required at any time, control unit 12 notes the last occurrence and duration of the other operations, the predicted timing of the next occurrence of the other operations and the latest measurements throughout the system. Control unit 12 can override or change {temporarily or permanently) the threshold value for a given operation if other criteria (eg measurements or other operations ) make it necessary.

Thus, for example, when a cooling operation has occurred, control unit 12 may check to see whether it is appropriate to adjust the ion generation operation and/or to operate the filter, and may instruct both of these to occur (even if the measured ion values do not yet justify any action) because information from previous situations for the system indicate that filtration and increased ions will be required shortly. In a different circumstance, if, after a cooling operation, the ion content is very high anyway, then the control unit 12 may determine that no filtration and no adjustment of the ion generation are necessary.

Sensor 14 has a simple low-cost and sturdy construction and yet it enables sensitive and accurate sensing of the amount of ions present in the water which flows past, thereby allowing the ion input to be controlled precisely and accurately to the level which is actually required at any given time in order to ensure cleansing of the water.

Typically, sensor 14 incorporates substantially pure platinum (for example 99%), but significently less pure platinum can be used, providing that the impurities are not toxic or otherwise undesirable. A water purifying system embodying the present invention provides continuous monitoring of the ion content of the water at the critical locations within the system and acts immediately any shortfall or reduction occurs in the ion content. This contrasts with prior art control arrangements which only monitor for consequential effects of ion content reductions and therefore can only, at best, restore the ion content to effective bacteria cidal levels after an interval of time during which there has been an opportunity for bacteria to proliferate in the system.

A water purification system embodying the present invention can be used in a wide variety of applications, for example in a domestic down water system 70 as illustrated in Figure 4 having an inlet pipe 71 supplying water from a rising main to a store tank 72 under the control of a ballcock valve 73. When required, water is supplied to the basin or bath taps 74 or to the shower 75 via an ionator cell 76 which is equivalent to ion generator 11 used in system 1. Unused water returns to tank 72.

Another application is a sealed cooling tower 80 as illustrated in Figure 5 in which pipework 81, carrying warmed water from a refrigeration system, passes over cooling elements 82 of a heat exchanger 88, in a cooling tower and then returns the water to the refrigeration system. Elements 81 are maintained cool by evaporative cooling of water in a circuit separate from the refrigeration system and pipework 80, this circuit having sprays 84 supplied from a tank 85 via an ionator cell 86 equivalent to ion generator 11.

Other applications of the invention include swimming pools and downwater or hotwater systems for domestic, commercial or industrial buildings.

Claims

1. A water purification system comprising: means to input silver ions into water; means to measure the amount of free ions in the water; means to vary the silver ion input in dependence on the output from the ion measurement means.

2. A system for bacteria control in a liquid reservoir, the system comprising: means to input silver ions into a liquid, for example water; means to measure the amount of free ions in the liquid; and means to vary the ion input in dependence on the output from the ion measurement means.

3. A system according to Claim 1 or 2, wherein the ion measurement means comprises means to measure any change in the amount of ions in the water.

4. A system according to Claim 3 comprising means to monitor the ion content in the water for any change in ion content correlated to a change in the silver ion generation.

5. A system according to any preceding Claim comprising means to input copper ions into water.

6. A system according to any preceding Claim, wherein the ions input means comprises means to generate ions electrolyticly.

7. A system according to any preceding Claim, comprising a chamber through which water flows, said ions input means being operable to input the ions into water as it flows through said chamber.

8. A system according to any preceding Claim, wherein measurement of the ion content, and/or of any change of the ion content, is effected upstream of the input of the ions.

9. A system according to any preceding Claim, wherein measurement of the ion content, and/or of any change of the ion content, is effected upstream and downstream of the input of the ions.

10. A system according to any preceding Claim, wherein the ions input means is operable to input ions into water at a rate in dependence on the amount of ions, and/or on any change of the ion content, measured in the water upstream and downstream of the input of the ions.

11. A system according to any preceding Claim, comprising means to measure the amount of ions, and/or any change in the ion content, in the water, said measurement means having a body of material containing platinum, which body is for exposure to a flow of water for which the ion content, and/or any change in the ion content, is to be measured, means to detect electrical charge in said body and means, to derive from the detection means, a value for the ion content, and/or any change in the ion content, in the water.

12. A system according to Claim 11, wherein the body of material comprises substantially pure platinum.

13 A system according to Claim 11 or 12, wherein the body of material is of elongate form.

14. A system according to Claim 11 or 12, wherein the body of material is substantially in the form of a plate.

15. A system according to any of Claims 11 to 14, wherein the body of material is substantially enclosed in an electrically insulating material other than that part which is for exposure to the flow of water.

16. A system according to any of Claims 11 to 15, wherein the charge detection means includes means to amplify and/or to measure any electrical voltage detected.

17. A system according to any preceding claim, comprising means to monitor the ion content, and/or any change in the ion content, in the water at at least one location and means to determine any modification in ion generation required in accordance with a detected change in ion content.

18. A system according to any preceding claim, comprising means to monitor for the occurrence of any one of a number of operations of the system, and means to determine any modification in ion generation required in accordance with the detection of the occurrence of an operation.

19. A system according to any preceding Claim, comprising means to store data on ion generation changes produced by ion content variations and/or by operations or routines of a system, means to predict any change in ion generation required due to a detected ion content variation and/or an operation or routine of the system, said prediction means utilising data from the storage means, and means to effect the change in ion generation determined by the prediction means.

20. Apparatus for the measurement of free ions in a fluid stream, the apparatus comprising a body of material containing platinum, which body is for exposure to a stream of fluid for which any change in the ion content is to be measured, means to detect electrical charge in said body and means to derive, from the output of the detection means, a value for any change in the ion content in the fluid.

21. Apparatus according to Claim 20, wherein the body of material comprises substantially pure platinum.

22. Apparatus according to Claim 20 or 21, wherein the body is of elongate form.

23. Apparatus according to Claim 20 or 21, wherein the body is substantially in the form of a plate.

24. Apparatus according to any of Claims 20 to 23, wherein the body of material is substantially enclosed in an electrically insulating material other than for that part which is for exposure to the flow of fluid.

25. Apparatus according to any of Claims 20 to 24, wherein the charge detection means includes means to amplify and/or measure any electrical voltage detected.

26. A method of purifying water comprising: inputting silver ions into water; measuring the amount of free ions in the water; varying the silver ion input in dependence of the measurement of ions in the water.

27. A method according to Claim 26, wherein the ion measurement stage comprises measuring any change in the amount of ions in the water.

28. A method according to Claim 27 comprising monitoring the ion content in the water for any change in ion content correlated to a change in the silver ion generation.

29. A method according to any of Claims 26 to 28, wherein the ions inputting stage comprises inputting copper ions.

30. A method according to any of Claims 26 to 29 comprising measuring the ion content and/or any change of the ion content upstream of the input of the ions.

31. A method according to any of Claims 26 to 30, comprising measuring the ion content, and/or any change in the ion content, upstream and downstream of the input of the ions.

32. A method according to any of Claims 26 to 31, comprising varying the ion input in dependence on measurement of ions, and/or any change of ions in the water upstream and downstream of the input of the ions.

33. A method according to any of Claims 26 to 32, comprising monitoring the ion content, and/or any change in the ion content, in the water at at least one location and determining any modification in ion generation required in accordance with a detected change in ion content.

34. A method according to any of Claims 26 to 33, comprising monitoring for the occurrence of any one of a number of operations of the system, and determining any modification in ion generation required in accordance with the detection of the occurrence of an operation.

35. A method according to any of Claims 26 to 3o, comprising storing data on ion generation changes produced by ion content variations and/or by operations or routines of a system, predicting any change in ion generation required due to a detected ion content variation and/or an operation or routine of the system, said prediction stage utilising stored data, and effecting the change in ion generation determined in the prediction stage.

36. A method of measuring the ion content, and/or any change in the ion content, in a fluid stream, the method comprising exposing a body of material containing platinum to a stream of fluid for which the ion content, and/or any change in the ion content, is to be measured, detecting electrical charge in said body and deriving, from the results of the detection stage, a value for the ion content of the fluid.

37. A water purification system substantially as hereinbefore described with reference to and/or as illustrated in any one or more of the Figures of the accompanying drawings.

38. Ion measuring apparatus substantially as hereinbefore described with reference to and/or as illustrated in any one or more of the Figures of the accompanying drawings.

39. A method of purifying water, the method being substantially as hereinbefore described with reference to and/or as illustrated in any one or more of the Figures of the accompanying drawings.