How to Detect and Prevent Wastage of Water? | Water Engineering

A considerable amount of water may be wasted in a distribution system because of leakage through pipe joints, fittings, etc.; careless use of water by the consumers especially in an unmetered water supply; theft of water through unauthorised water connections; and other miscellaneous reasons. As far as possible the wastage of water in a distribution system should be minimum. It is therefore necessary to detect and prevent the wastage of water in a distribution system.

Methods of Detecting Wastage of Water in a Distribution System:

The various methods which may be adopted to detect the wastage of water in a distribution system are as follows:

(i) Water Waste Surveys:

The water waste surveys are carried out with the following objects:

(i) To discover blown-out joints in mains,

(ii) To find out unauthorized users of water, and

(iii) To find out the water wasted by unmetered consumers.

In order to carry out water waste surveys a section of the distribution system is isolated from the rest by proper manipulation of valves so that all the water in the isolated section passes through a single pipe. The flow of water in the pipe is measured and if found more than its normal capacity, the section is further divided into sub-sections and the procedure repeated, till the exact portion of the distribution section having high consumption of water is located.

The necessary measures are then taken to reduce the wastage of water and bring it down to the permissible limit. The measurements are carried out at night time or during early hours of morning when domestic consumption is the lowest.

(ii) Location of Leaks:

Leaks in water supply pipes are undesirable as in addition to the large amount of wastage of water they may undermine pavements and other structures close to the pipes. The maximum permissible limit for wastage of water through leaks in water supply pipes may be taken as 11.60 litres per hour per centimeter diameter of pipe per kilometer length. For instance, the maximum permissible limit for wastage of water through 5 km long 30 cm diameter pipe would be 1740 litres per hour.

For locating leaks in water supply pipes following methods may be used by:

(a) Direct observations

(b) Using sounding rods

(c) Plotting hydraulic grade line

(d) Using waste-detecting meters.

(a) Direct Observations:

In the method of direct observations, the presence of green grass during drought, a wet soft spot on the ground, or an emergence of a spring at an odd place may serve as some indication of there being leaks in the water supply pipe lying below the ground in that area. However, for determining the exact location of leaks at such places other methods will have to be employed.

(b) Using Sounding Rods:

In this method a sharp-pointed steel rod is thrust into the ground along the pipeline and pulled up for inspection. If the pointed edge of the steel rod has become wet, it indicates the presence of leaks in the pipeline.

In another method a metal rod is inserted into the ground at the suspected portion in such a way that it makes contact with the pipe. If there is a leak in the pipe the sound of the water escaping through the leak can be heard by placing the ear against the rod, or by means of an amplifying device such as aqua phone (similar to telephone) or sonoscope (similar to stethoscope). These devices can enlarge or magnify sound to the extent of 10000 times the original sound. Thus, when such devices are used, the sound of escaping water can be heard even when there is no actual contact between the rod and the pipe.

(c) Plotting Hydraulic Grade Line:

In this method the pressures at various points along the suspected length of pipeline are measured and the hydraulic grade line is plotted. The appearance of any ‘kink’ or sudden change in slope in the hydraulic grade line will indicate the location of leak in the pipeline.

(d) Using Waste-Detecting Meters:

A waste-detecting meter does not actually record the quantity of water going to waste but it only measures any unusually high flow passing through a water supply pipe during a period of low consumption such as during night time or early hours of morning.

This unusual excess flow in a section of pipeline will indicate the leakage of water from the pipeline in that section, provided it is reasonably established that the unusually high flow is not due to any other demand at that time in the distribution area served by that section of pipeline.

In this method a section of the distribution system to be tested is isolated from the rest by manipulating the valves so that water is supplied to this section only. At the head of the water main supplying water to this section a waste- detecting meter is fitted which records the flow of water supplied to this section. The supply of water to each of the sub-sections of this section is then progressively stopped.

With the stoppage of supply of water to each sub-section the flow of water in the water main would drop and the same is recorded by the waste- detection meter. The reduction in the flow recorded by the waste-detection meter at stoppage of water supply to each sub-section is compared with the flow in the corresponding sub-section based on the consumption of water in the area served by the sub-section. If the stoppage of water supply to any sub-section causes a disproportionately large reduction of flow, it indicates the presence of a leak in that sub-section.

Deacon’s meter (or Deacon’s waste water meter) is a most widely used waste- detecting meter as it is quite sensitive and accurate. The water flowing through the meter forces down a brass disc otherwise held in closed position by a counter weight.

The movement of the disc is in proportion to the quantity of water flowing through the meter, and this movement of the disc is conveyed through a rod attached to the disc and carrying a pen (or pencil) which moves vertically up and down on a calibrated graph paper mounted on a drum and moving horizontally with time. The quantity of water flowing per unit time through the meter is thus automatically recorded.

The method of using waste-detecting meters is very scientific and useful for detecting leaks in a water distribution system and hence it is widely used. However, it has a few drawbacks such as high cost of operation by keeping extra staff working during night-time, installation of additional valves and making many cut-outs for inserting meters, etc. In spite of these drawbacks the method is widely used for detecting leaks in water supply pipes and thus results in large-scale reduction in wastage of water.

After detecting the exact location of leaks in water supply pipes necessary measures should be taken to rectify the same so that the wastage of water through leaks may be curtailed.

Measures to Prevent Wastage of Water in a Distribution System:

In order to reduce the wastage of water in a distribution system the following preventive measures may be adopted:

1. The design of layout of distribution system should be such that each branch line serves about 2000 to 3000 persons only. Such a design of layout makes it easier to locate the leaks in the pipeline.

2. The supply of water should be preferably through meters, so that the consumers are careful and will use water economically.

3. The public should be made to understand the importance of water and its economical use. For this purpose a regular campaign should be arranged which may be in various forms such as articles in local newspapers, posters at public places, seminars and discussions, lectures by leaders, radio talks, television, etc.

4. The fittings used in joining the pipes should conform to the standard requirements.

5. A vigilance gang should be maintained by the local authority for house to house inspection to detect unauthorised water connections as well as careless consumers. Legal actions should be taken against the persons having unauthorised water connections to stop such recurrences in future. Similarly heavy penalty should be imposed on careless consumers.

6. The service connections of distribution system should be carried out only by authorised plumbers.

7. It is believed that the intermittent system of supply of water reduces the amount of wastage of water and hence the same may be adopted.

8. Leaks (if any) in water supply pipes should be located and rectified immediately to stop the wastage of water.