GB2604581A

GB2604581A - Water management apparatus

Info

Publication number: GB2604581A
Application number: GB2102212.4A
Authority: GB
Inventors: Charles Mead Jeremy
Original assignee: Individual
Current assignee: Individual
Priority date: 2021-02-17
Filing date: 2021-02-17
Publication date: 2022-09-14
Also published as: GB202102212D0

Abstract

A water management apparatus 10 for location underground, comprising a water chamber 12 having a water permeable walls 14 such that, in use, water can pass from the chamber through the walls, and a water inlet (18, Fig. 2) for feeding water into the chamber. There may be a maintenance hatch 22. Water is arranged to pass from the water retaining chamber through the one or more water permeable walls. The walls may comprise reticulated chambers, for example a reticulated foam passage 32, to affect the rate of water leaving the chamber e.g. to allow the chamber to act as a water storage and attenuation device during heavy rainfall. There may a silt trap and/or filtering means e.g. a carbon filter. A second embodiment (see Fig. 3) include a grey water recovery and storage system, with a pump, filter sensors and wireless control system for reusing grey water e.g. to flush toilets. The system may be modular including multiple cylindrical sections which can be connected to form larger tanks (Fig. 7).

Description

Water Management Apparatus

Field of the Invention

The present invention concerns a water management apparatus. More particularly, but not exclusively, this invention concerns a water management tank for providing a soakaway. The invention also concerns a water management tank and water recycling system.

Background of the Invention

When building extensions, new houses and buildings, it is necessary to put in place water management systems to deal with water run-off from the buildings. Common approaches include installation of soakaways, which include gravel lined pits or trenches, and soakaway crates, which are porous crates installed in the gravel lined pits or trenches in order to receive and contain water as it soaks into the surrounding environment. Presently, when digging pits or trenches, it is necessary for a worker to enter the pit or trench in order to lay the gravel bed, install the soakaway crates, and potentially wrap the crates with geotextile material. This can be hazardous, with a risk of collapsing side walls. In order to mitigate this risk, health and safety regulations govern the maximum pit depth allowable without side wall reinforcement. Such reinforcement can be costly and time consuming, and the risk of collapse may remain, albeit reduced. The control of material and use is difficult to ensure as the product is infilled before inspection and the quality of gravel and soakaway crates may not meet the designed regulations. There are also significant challenges when seeking to maintain present arrangements.

The present invention seeks to mitigate the above-mentioned problems.

Summary of the Invention

The present invention provides, according to a first aspect, a water management apparatus comprising one or more water permeable walls and a water retaining chamber, wherein water is arranged to pass from the water retaining chamber through the one or more water permeable walls, and a water inlet arranged to feed water into the water retaining chamber.

The one or more water permeable walls may enclose the water retaining chamber. There may be a water-retaining tank located within the water retaining chamber. The water retaining chamber may comprise one or more openings or passageways through which water may pass into the water permeable walls. The one or more openings may be located towards the bottom of the water retaining chamber if the water management apparatus only intended to act as a soakaway, or may be located towards the top of the water retaining chamber if the water management apparatus is intended to store water, for example for water recycling purposes. The water management apparatus may form a single unit. The single unit may be easily transported, and/or easily installed. The installation may comprise the steps of digging a pit and lowering the unit into the pit. The base of the pit may be lined with gravel or concrete before the unit is lowered into the pit. The step of lining the pit with gravel may be undertaken by mechanical apparatus, such as a digger, without requiring an operator to enter the pit. The water management apparatus may include one or more lifting eyes to allow easy lifting and lowering into a pit.

In an alternative arrangement, the water management apparatus may be modular, with the water retaining chamber and one or more water permeable walls being installed individually and then connected up to allow water to pass from the water retaining chamber through the one or more water permeable side walls. A modular arrangement may allow for a network of water retaining chambers and water permeable walls to be created, for example to provide a large capacity system for dealing with water management demands of a housing estate, business development, or road system.

The water-retaining chamber may have a volume from 500 litres to 15,000 litres, for example 2500 litres. The overall capacity of the water management apparatus, including water which may be held in the water-retaining chamber and one or more water permeable walls, may be from 500 litres to 20,000 litres, for example 5000 litres.

The water inlet may be connected to a land drainage or guttering system, such that rainwater passes through the water inlet into the water management apparatus and/or a grey water recovery system to receive water from showers, baths, washing machines etc.. Alternatively or additionally, the water inlet may be connected to a water outlet of a sewage treatment apparatus. The water inlet may comprise a non-return valve, such that water is prevented from leaving the water management system via the water inlet, for example when the water retaining chamber reaches capacity.

The water management apparatus may comprise a silt trap. The silt trap may be associated with the water inlet, such that prior to water entering the water retaining chamber, the water passes through the silt trap. Such an arrangement may reduce the amount of solid bodies, for example stones, leaves, etc. entering the water retaining chamber of the water management apparatus. The silt trap may include a removable filter to allow easy cleaning. The removable filter may be a metal mesh, for example a stainless steel basket.

The water management apparatus may comprise a filter, for example a carbon filter and/or limestone natural water filter. Such a filter may be associated with the water inlet, such that prior to water entering the water retaining chamber, the water passes through the filter. Such an arrangement may remove contaminants and/or alter the pH of water entering the central volume of the water management apparatus. Such an arrangement may reduce the environmental impact of water passing through the water management apparatus into the local area.

The water management apparatus may be cuboid in shape, with four water permeable side walls enclosing a central volume. The water management apparatus may comprise more than four water permeable side walls, or may comprise a curved or circular water permeable side wall. The water management apparatus may comprise a water permeable base wall. The water permeable walls may comprise reticulated chambers, for example a reticulated foam and a geotechnical fabric, for example a fabric sealed bag, may surround the reticulated foam. The geotechnical fabric may be a woven, or non-woven fabric, and the specific material may be chosen to provide the desired fluid transfer rate into the surroundings of the water management apparatus. The water permeable walls may comprise a carbon filter, for example a felted carbon filter. The carbon filter may be replaceable, for example via a maintenance worker entering the water management apparatus and replacing the carbon filter. The construction and density of the reticulated chambers may be chosen to provide the desired soak rate of water into the local environment. Such an arrangement will allow water to be stored within the water management apparatus -4 -during heavy rainfall, and dispersed into the local environment in a controlled manlier. The water permeable side walls may include at least one outer surface wrapped with a geotextile fabric. The water permeable side walls may comprise reticulated chambers wrapped in a geotextile fabric.

The water management apparatus may comprise one or more water permeable bags filled with gravel, or other suitable fragmented loose material. The one or more water permeable bags may be attached to a side outrig plate, and may be filled with back fill material during the installation process. The water permeable bags filled with loose material may be provided abutting the external side of a water permeable side wall of the water management apparatus. The water permeable bags filled with loose material may be located such that, when installed in a pit, the water permeable bags abut the edges of the pit.

Water entering the water management apparatus may be retained in the water-retaining chamber, for example by locating the passageways into which water passes into the water permeable walls towards the top of the water retaining chamber. The portion of the water retaining chamber located below the passageways may be the water storage portion of the water retaining chamber. When the storage portion of the water-retaining chamber is full, water entering the water management apparatus may pass into and through a water retaining wall, through a water permeable bag filled with loose material, and into the side wall of a pit. In such a way, the water management apparatus provides a controlled soakaway into the ground local to the water management apparatus.

The water management apparatus may comprise a top wall. The top wall may be flat, curved, an arched surface, or a dome. The top wall may be shaped to allow structural reinforcement to be added over the water management apparatus during installation if heavy loading is required. An arched surface or dome may be stronger than a flat top wall. The top wall may enclose the central volume of the water management apparatus. The top wall may allow the water management apparatus to be buried in a pit, with, for example, grass or other landscaping covering the top wall.

The top wall may include an inspection and/or maintenance hatch to allow access to the central volume of the water management apparatus, for example providing full access to allow a maintenance worker to enter the water retention chamber. The inspection and/or maintenance hatch may extend upwardly from the top wall to allow -5 -access even when the top wall is buried some depth underground. The inspection and/or maintenance hatch may include line fixings for maintenance workers to attach safety lines to when entering the water retention chamber.

The water management apparatus may comprise an overflow. The overflow may comprise a pipe extending from the central volume of the water management apparatus. The overflow pipe may include an air vent. The air vent may extend in to a maintenance access chamber associated with the maintenance and/or inspection hatch. Should the capacity of the water management apparatus be reached, the overflow allows water to leave the water management apparatus in a controlled way.

The water management apparatus may comprise a water recirculation system.

The water recirculation system may comprise a pump. The pump may be arranged to pump water from the central volume of the water management apparatus through a water outlet. The water passing through the water outlet may be used for grey water purposes, such as flushing toilets, watering gardens, washing machines, and cleaning cars. The pump may be arranged to pump water from the water retaining chamber, for example the storage portion of the water retaining chamber. The water recirculation system may comprise a filter, through which water leaving the water management tank via the water outlet passes, to remove potential contaminants from the water.

The water management apparatus may comprise a control unit. The control unit may be arranged to control the operation of the water recycling system. The water management apparatus may comprise one or more sensors arranged to detect one or more of the volume of water entering the water management apparatus, the volume of water present in the water management apparatus, and/or the volume of 25 water removed from the water management apparatus by the water recycling system. According to a second aspect of the invention there is also provided a method of installing a water management apparatus according to the first aspect of the invention, the method comprising the steps of: digging a pit of sufficient size to contain the water management apparatus, laying a bed of loose material at the base of the pit, lowering the water management apparatus into the pit such that the water management apparatus sits on the bed of loose material, and surrounding the water management apparatus with one or more water permeable bags of loose material. The method may further include the step of covering a top wall of the water management -6 -apparatus with soil such that the water management apparatus is buried in the pit. The method may include the step of connecting the water inlet of the water management apparatus to a land drainage or guttering system, such that rain water is fed into the water management apparatus, or grey water recovery system to receive water from showers, baths, washing machines etc. According to a third aspect, the invention provides a method of recycling water, the method comprising the steps arranging for rain water to be directed into a water management apparatus according to the first aspect of the invention, and pumping water from the central volume of the water management apparatus, through a water outlet and into a grey water recycling system. The method may comprise the steps of controlling the water management apparatus electronically, for example with the use of an electronic control unit. The method may comprise the step of monitoring the usage of grey water, and may include the step of communicating that information to a user of the water management apparatus. Various conventional monitoring apparatus may be used, for example to provide information local to the water management apparatus, or to send monitoring apparatus to a smart device, for example a phone or tablet of a user.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: Figure 1 shows an end cross sectional view of a water management apparatus view according to a first embodiment of the invention, Figure 2 shows a front cross sectional view of the water management apparatus of figure 1; Figure 3 shows a front cross sectional view of a water management apparatus according to a second embodiment of the invention; -7 -Figure 4 shows a schematic view of a water recycling system according to a third embodiment of the invention; Figure 5 shows a cross-sectional view of a water permeable wall which may be present in either or both of the first or second embodiment of the invention; Figure 6 shows a cross-sectional view of a reticulated foam and carbon filter water inlet, and Figure 7 shows a schematic view of a water management apparatus according to a third embodiment of the invention.

Detailed Description

Figures 1 and 2 show cross sectional views of a water management apparatus 10, the water management apparatus configured to control the flow of rain and/or drainage water into the surroundings of the water management apparatus 10. The water management apparatus 10 comprises a water retaining chamber 12, which is enclosed with four water permeable side walls 14, and has a water permeable base 16. A water inlet 18 feeds water from a ground drainage and/or guttering system into the water retaining chamber 12, where the water will be retained for a period of time prior to passing through the water permeable side walls 14 and water permeable base 16 into the surroundings of the water management apparatus 10. As can be seen, the water management apparatus 10 has an arched roof 20 which extends above the water retaining chamber 12, and allows the water management apparatus 10 to be buried underground. The roof 20 includes an access hatch 22, with an opening which allows access to the water retaining chamber 12 for maintenance or other service requirements. Various safety apparatus may be added to the access hatch, for example a safety line connection point 23, to which a maintenance worker can connect a safety line prior to entering the water retaining chamber 12. An overflow outlet 24 is provided towards the arched roof 20 and above the water retaining chamber 12, to allow a controlled overflow path should water enter the water retaining chamber 12 at a faster rate than the water passes through the water permeable side walls 14 and the water permeable base 16 for an extended period of time meaning that the capacity of the water management apparatus 10 is reached. The -8 -water permeable side walls 14 and water permeable base 16 comprise a reticulated core surrounded by a water permeable fabric. The reticulated core comprises a series of openings though which water can pass, and is designed to allow a limited amount of water pass through in a set time period. A cross-sectional view of the reticulated core is shown in figure 5. By providing differently configured reticulated cores, the rate at which water passes from the water retaining chamber 12 into the surroundings of the water management apparatus can be altered. Factors which influence the choice of reticulated core include the capacity of the surroundings to absorb water without presenting a flood risk, and also the expected maximum rainfall in the area which feeds water into the water management apparatus. A gravel bed 26 will be laid in a pit prior to installation of the water management apparatus 10, which will also influence and help control the rate at which water passes from the water retaining chamber 12 into the surroundings of the water management apparatus 10. Fabric bags 28 are also provided extending from the external surface of the side retaining walls 14, which are filled with loose fragmented material, for example gravel or backfill from creating the pit, which further control the passage of water from the water retaining tank 12 into the surroundings of the water management apparatus.

The water retaining chamber 12 comprises a water impermeable lining 30, with reticulated foam passages 32 through which water passes from the water retaining chamber 12, into in the water permeable side walls 14 and water permeable base 16. The reticulated foam passages 32 also include at least one carbon filter, and are shown in greater detail in figure 6. Controlling the flow of water into the water permeable side walls 14 and water permeable base 16 with restricted access further retards the passage of water into the surroundings of the water management apparatus 10 and reduces the pressure of the water passing through the water permeable side walls 14 and water permeable base 16. The pressure within the water permeable side walls 14 and water permeable base 16 should remain relatively constant, regardless of the water level within the water retaining chamber 12, thus maintain a constant soakaway rate. The reticulated foam passages 32 are located towards the bottom of the water retaining chamber 12, so that in the event of an extended dry period, the water retaining chamber 12 can empty out. Further features, such as filters associated with the water inlet 18, sensor units, etc. may be added to the embodiment shown in -9 -figures 1 and 2, and will be described in more detail with reference to a second embodiment of the invention shown in figure 3.

In order to install the water management apparatus 10, a pit is dug which can fully contain the water management apparatus 10. A bed of gravel 26 is laid at the bottom of the pit and the water management apparatus 10 placed on top. The water inlet 18 is connected to a land drainage and/or guttering system, and the water outlet 24 is connected to an overflow dispersal pipe. The fabric bags 28 are filled with loose material, for example backfill from creating the pit or additional gravel. The remaining space to the sides of the water management apparatus 10 are backfilled, and the roof 24 covered over, leaving only the access hatch 22 accessible from above.

Figure 3 shows a water management apparatus 110 which both controls the flow of rain and/or drainage water into the surroundings of the water management apparatus 110 and provides a water recycling system, for example for use in toilets or other common grey water uses. The basic structure of the water management apparatus 110 is similar to that shown and described with respect to figures 1 and 2, and the water management apparatus 10. Where obviously like for like features are present, the skilled person will recognise them as such and duplicated descriptions are not necessary, and/or may be indicated simply by the addition of the prefix "1" to a reference numeral. For example, "XX" in the first embodiment would be "1XX" in the second embodiment, such as the outlet in the second embodiment 124 corresponding to the outlet in the first embodiment 24. A water retaining chamber 112 is surrounded by water permeable side walls 114. However, in contrast with the first embodiment, in the second embodiment there is no water permeable base. Also, the inlets 132 which allows the passage of water from the water retaining chamber 112 into the water permeable side walls 114 are located towards the top of the water retaining chamber 112. Therefore, the water retaining chamber 112 includes a storage portion for water entering the water management apparatus 110 via the water inlet 118. The water inlet 118 includes some additional features, including a silt trap 140, with for example a removable stainless steel mesh, and a limestone filter 142, arranged such that solid debris is filtered out of the water entering the water management apparatus 110 by the silt trap 140, and the pH of the water entering the water management apparatus 110 is adjusted by passing through the limestone filter 142. Both the silt trap 140 and limestone filter 142 are accessible via a maintenance -10 -hatch 144. A sensor (not shown) is also associated with the water inlet 118 and arranged to detect the volume of water entering the water management apparatus 110 through the water inlet 118. A non-return valve 148 is also included in the water inlet 118 to prevent water passing back through the water inlet 118 when the water management apparatus 110 is full. The water management apparatus 110 includes a water recycling system including a pump unit 150 which is arranged to take water from a feed pipe 152 located at the bottom of the water retention chamber 112, and pump the recovered water into a grey water system, for example for flushing toilets or other common grey water uses. One or more filters may be arranged such that the recovered water is further filtered prior to exiting the water management apparatus, and/or additional filters may be provided in the grey water system. A sensor 152 is linked to the pump unit 150 and arranged to monitor the volume of water being pumped through the pump unit. Other sensors may be located in the water management apparatus 110 and arranged to detect various parameters such at the volume of water contained within the water retention chamber 112, and the pH of water contained within the water retention chamber. All of the sensors may be arranged to communicate, either in a wired arrangement or wirelessly, with a control unit 154. The control unit 154 may be local to the water management apparatus 110, or remote, for example a remote workstation, or smart device such a phone or tablet.

The control unit 154 is arranged to collate and display information to a user, for example including the volume of water presently in the water retention chamber, and how much water has been pumped into the grey water system over a period of time. The control unit 154 may also display how much money has been saved by use of grey water, rather than use of mains water.

The water management apparatus 110 is installed in a similar way to first embodiment, with the additional steps of connecting the grey water recycling system up, and providing power to the pump 150 and various sensors as required.

Figure 4 shows a water management system comprising a water management apparatus 110 as described with reference to figure 3, and a grey water system 200.

The grey water system 200 is connected to both the water management apparatus 110 and a mains water system 202 via a switching unit 204. The switching unit 204 is arranged to feed water from the water management apparatus 110 into the grey water system 200 when the water management apparatus 110 contains a suitable volume of water. When the water management apparatus is empty, for example due to a lack of rain and/or extended use of the grey water system, the switching unit 204 is arranged to switch the feed from the water management apparatus 110 to the mains water system 202. When the water management apparatus 110 has refilled to a sufficient level, the switching unit 204 switches the feed back to the water management apparatus 110. The switching operation is controlled via the control unit 154. Figure 5 shows a cross section of a water permeable side wall 14. The side wall 14 is in fluid connection with the water retaining chamber 12 via the reticulated foam passage 32. The reticulated foam passage includes a carbon filter 50 clamped in position, such that the carbon filter 50 can be removed and replaced as required. As can be seen, the water permeable side wall 14 comprises a series of reticulated passages formed of a plurality of different diameter pipes. Some of the pipes are arranged to provide storage to the water as is passes through the water permeable side wall 14, and some of the pipes are arranged to provide no storage water flow. The first series of pipes 52 have a diameter of 55mm, a second series of pipes 54 have a diameter of 110mm, and a third series of pipes 56 have a diameter of 45mm. All of the pipes are made of uPVC material. The pipes are arranged with various spacings separating them, ranging from 3mm to 15mm.

Figure 6 shows an alternative arrangement of the reticulated foam passageway 32. A removable and replaceable foam filter 60 is clamped at a distal end of the foam passageway 32, the foam filter 60 having a pores per inch (ppi) between 50 and 60 ppi. The carbon filter 50, with a thickness of 25mm, is sandwiched between two additional reticulated foam portions 62, the additional reticulated foam portions 62 also with a pores per inch of between 50 and 60 ppi. The various portions of foam and carbon filter 50 are wrapped in a geotextile fabric 64, all of which is housed within an external filter wall 66 which comprises glass-reinforced plastic material. The foam passageway 32 further includes a support strut 68, which holds the foam passageway 32 in position with respect to the water permeable wall 14 into which the foam passageway 32 supplies water.

Figure 7 shows an alternative embodiment of the invention, where a large central cylindrical water retention tank 70 is arranged to be fluidly connected to water permeable walls 72 which are spaced from the water retention tank 70. The fluid connection is via filter containing passageways 74, and in a similar way to described -12 -with reference to the other embodiments of the invention, the water retention tank holds a certain amount of water, and also allows water to pass into the local surroundings via the water permeable walls 72 in a controlled manner. The arrangement may be modular, allowing several water retention tanks and water permeable walls 72 to be connected up to increase the capacity of the system. This may be useful in housing estates and other large developments, where the need to control water soakaway is high. Conveniently, the water retention tanks and water permeable walls may be located underneath roadways etc. and include an access hatch 76 to maintenance purposes.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. For example, the water inlets of the water management apparatus have been described as connected to a ground drainage or guttering system. The water inlets may alternatively or additionally be connected to receive grey water from showers, washing machines etc., and/or a water outlet of a sewage treatment apparatus.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

-13 -Claims 1. A water management apparatus comprising one or more water permeable walls and a water retaining chamber, wherein water is arranged to pass from the water retaining chamber through the one or more water permeable walls, and a water inlet arranged to feed water into the water retaining chamber.
2. A water management apparatus as claimed in claim 1, wherein the one or more water permeable walls enclose the water retaining chamber.
3. A water management system as claimed in claim 1 or claim 2, further comprising a water-retaining tank located within the water retaining chamber.
4 A water management system as claimed in any preceding claim, wherein the water management apparatus forms a single unit.
5. A water management apparatus as claimed in any preceding claim, wherein the water inlet comprises a non-return valve, such that water is prevented from leaving the water management system via the water inlet.
6 A water management system as claimed in any preceding claim, wherein the water management apparatus comprise a silt trap.
7. A water management apparatus as claimed in claim 6, wherein the silt trap is associated with the water inlet, such that prior to water entering the water retaining chamber, the water passes through the silt trap.
8 A water management apparatus as claimed in any preceding claim, further comprising a filter associated with the water inlet, such that prior to water entering the water retaining chamber, the water passes through the filter.
9. A water management apparatus as claimed in any preceding claim, wherein the one or more water permeable walls comprise reticulated chambers.
-14 - 10. A water management apparatus as claimed in claim 9, wherein the one or more water permeable walls comprise a reticulated foam.
11. A water management apparatus as claimed in claim 10, wherein a geotechnical fabric surrounds the reticulated foam.
12. A water management apparatus as claimed in any preceding claim, wherein the one or more water permeable walls comprise a carbon filter.
13. A water management apparatus as claimed in any preceding claim, further comprising one or more water permeable bags filled with a fragmented loose material.
14. A water management apparatus as claimed in any preceding claim, further comprising a curved top wall.
15. A water management apparatus as claimed in any preceding claim, further comprising an inspection and/or maintenance hatch to allow access to the water retention chamber.
16. A water management apparatus as claimed in any preceding claim, further comprising an overflow.
17. A water management apparatus comprising a water recirculation system.
18. A water management apparatus as claimed in claim 17, wherein the water recirculation system comprise a pump arranged to pump water from the water retention chamber through a water outlet.
19. A water management apparatus as claimed in claim 18, wherein the water recirculation system comprises a filter.
20. A water management apparatus as claimed in any preceding claim, further comprising a control unit.
21. A method of installing a water management apparatus according to claim 1, the method comprising the steps of: digging a pit of sufficient size to contain the water management apparatus, laying a bed of loose material at the base of the pit, lowering the water management apparatus into the pit such that the water management apparatus sits on the bed of loose material, and surrounding the water management apparatus with one or more water permeable bags of loose material
22. A method of recycling water, the method comprising the steps of: arranging for grey water and/or rain water to be directed into a water management apparatus according to claim I, and pumping water from the central volume of the water management apparatus, through a water outlet and into a grey water recycling system
23. A method of recycling water as claimed in claim 22, the method comprising the step of controlling the water management apparatus electronically.
24. A method of recycling water as claimed in claim 22 or 23, the method comprising the step of monitoring the usage of grey water.