1 WATER HOSE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a water hose adapted for 5 conveying a fluid. 2. The Prior Arts Water hoses are used for conveying water or other fluids, and specifically fabricated with different materials in accordance with the desired purpose and pressures to be withstood. For example, a typical household water hose is made 10 of plastic material and configured with a tubular shape having a round-shaped cross-section, and a typical fire hose is a high-strength flexible water hose made of a plurality of composite materials. As to a water pipeline used for conveying water over a long distance, it is usually made of metal materials. Generally, the water hoses used for household purpose or temporarily 15 used in working environments are flexible and made of plastic materials, and can be used indoors or outdoors. When such a water hose is used outdoors and is laid over a long distance, it is often run over by vehicles or stepped over by pedestrians, such that the outflow of the water is often unsmooth. Further, when such a water hose is not in use or to be collected for reservation or carrying, the 20 water hose is usually rolled up into a roll. However, when rolled up, the conventional water hose having a round-shaped cross-section is still bulky and inconvenient for carrying, and occupies a large space for conservation. SUMMARY OF THE INVENTION A primary objective of the present invention is to provide solution for 25 solving the foregoing problems of the above discussed flexible water hoses. Accordingly, the present invention provides a water hose. The water hose is configured with a flat shape, so that when the water hose is not in use, it can be rolled up into a small roll, which is convenient for conservation and carrying. According to an embodiment of the present invention, the water hose 30 includes a rib longitudinally extending along a passage channel of the water hose, for providing a support when water hose endures an external pressure, so as to 2 avoid the passage channel of the water hose from being clogged and maintain the passage channel of the water hose clear. According to an embodiment of the present invention, the water hose includes a sleeve assembled over a hose body of the water hose. The sleeve 5 provides visional ornamental effect and also provides convenience that when the water hose is contaminated the sleeve can be removed or exchanged for cleaning. Therefore, the present invention provides a water hose including a hose body, and a sleeve. The hose body is made of an elastic and flexible material, 10 and is configured with a flat shape longitudinally extending for a certain length. When the hose body is not in use and is free of any external force, a radial cross section of the hose body substantially presents a flat shape. The hose body includes at least one rib. The rib extends along the longitudinal length of the water hose inside a passage channel defined in the hose body. When water is 15 introduced into the passage channel of the water hose, the water applies a water pressure against an inner sidewall of the passage channel so that the hose body is bloated by the water pressure, and therefore the radial cross-section of the hose body substantially presents a round shape. When an external force is applied on the water hose, the rib provides a support on the inner sidewall of the 20 passage channel so as to avoid the passage channel of the water hose from being clogged and maintain the passage channel of the water hose clear. Since the water hose is flat-shaped, when it is not in use, it can be conveniently rolled up into a roll for conservation and carrying. The sleeve is configured for allowing the hose body to be movably 25 assembled therethrough. The outer surface of the sleeve can be provided with logos of the manufacturer or ornamental patterns. Alternatively, the water hose including three ribs as discussed above, in which two ribs are configured at one side of the passage channel and the other one is configured at an opposite side of the passage channel. 30 3 BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be apparent to those skilled in the art by reading the following detailed description of preferred embodiments thereof, with reference to the attached drawings, in which: 5 Fig. 1 is a perspective view of a water hose according to an embodiment of the present invention; Fig. 2 is a perspective exploded view of the water hose illustrating the assembly of the hose body and the sleeve according to an embodiment of the present invention; 10 Fig. 3 is a cross-sectional view of the hose body of the water hose illustrating the operation status of the water hose when the water hose is not in use; and Fig. 4 is a cross-sectional view of the hose body of the water hose illustrating the operation status of the water hose when the water hose is bloated 15 by a pressure of water introduced inside the passage channel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, 20 together with the description, serve to explain the principles of the invention. Fig. 1 is a perspective view of a water hose according to an embodiment of the present invention. Fig. 2 is a perspective exploded view of the water hose illustrating the assembly of the hose body and the sleeve according to an embodiment of the present invention. Referring to Figs. 1 and 2, the present 25 invention provides a water hose including a hose body 1, and a sleeve 2. The hose body 1 is made of an elastic and flexible material such as plastic or rubber. The hose body 1 is configured longitudinally extending for a certain length such that when the hose body 1 is not in use and is free of any external force, a radial cross-section of the hose body 1 substantially presents a flat shape. The hose 30 body 1 includes at least one rib 11. The rib 11 extends along a longitudinal length of the water hose 1 and inside a passage channel defined in the hose body 1.
4 Preferably, as shown in Fig. 3, the hose body 1 includes three ribs 11. Two ribs 11 are configured at one side of the passage channel and the other one rib is configured at the other side of the passage channel. Fig. 4 is a cross sectional view of the hose body of the water hose illustrating the operation status 5 of the water hose when the water hose is bloated by a pressure of water introduced into the passage channel. When a water is introduced into the passage channel of the water hose 1, the water applies a water pressure against an inner sidewall of the passage channel so that the hose body 1 is bloated by the water pressure, and therefore the radial cross-section of the hose body 1 10 substantially presents a round shape as shown in Fig. 4. The sleeve 2 is a sleeve member made of a waterproof material (e.g., a waterproof fabric). The sleeve member has two longitudinal ends communicable with each other. Preferably, at least one side in width of the sleeve 2 is heat sealed by a high frequency welding technology to form a sealing portion 22. The 15 sleeve 2 is configured for allowing the hose body 1 to be movably assembled therethrough. In such a way, the user can conveniently remove or exchange the sleeve 2 when he desires to do so (for example the sleeve 2 is contaminated or he desires to change a sleeve with different patterns). Preferably, the sleeve 2 has an outer surface having a pattern 21 configured thereon. The pattern 21 can 20 be a logo of the manufacturer or any company, or otherwise a simple symbol or color shade. When the water hose is in use, one end of the water hose is coupled with a water source (e.g., a water tap), and the other end of the water hose is coupled with, for example, a water sprayer, a water sprinkler, or a joint. When water is 25 introduced into the passage channel of the hose body 1 of the water hose, the water applies a water pressure against the inner sidewall of the passage channel so that the hose body 1 is bloated by the water pressure, and therefore the radial cross-section of the hose body 1 substantially presents a round shape. When an external force is applied on the water hose (e.g., a vehicle runs over the water 30 hose or a pedestrian steps on the water hose), the ribs 11 provides a support on the inner sidewall of the passage channel so as to avoid the passage channel of the water hose from being clogged and maintain the passage channel of the 5 water hose clear. Further, since the water hose is flat shaped, when it is not in use, it can be conveniently rolled up into a roll for conservation and carrying. Although the present invention has been described with reference to the preferred embodiments thereof, it is apparent to those skilled in the art that a 5 variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims. 10