The process of distributing treated water to the consumers is called water distribution system. The distribution system includes pumps, reservoirs, valves, water meter, pipe fittings, etc. The cost of the distribution system is about 40-70 % of the total of the entire scheme.
The aim of a good water distribution system is to supply water to all the consumers whenever required in sufficient quantity with required pressure without any leakage.
1.Requirements of good water distribution system
- The system should be economical to maintain and operate.
- Sufficient water should reach to all consumers.
- It should be able to draw enough water during an emergency like fire fighting.
- The system should be watertight and leakage should be least as possible.
- Any types of contamination of water should not occur during the distribution.
- It should not be laid below the sewer lines as far as possible.
- The system should have required pressure that it conveys water adequate but the pressure should not be high causing the bursting of pipes and fittings.
- The distribution layout should be such that it should supply water even during repair and maintenance time.
2.Methods of water supply of Water Distribution System
There are two types of supplying water.
i. Continuous system
ii. Intermittent system
- Continuous system
This is the best method in which the water is supplied to the community during all 24 hours of a day.
In this system, a sufficient amount of water is always available for consumers to use and also for an emergency like a fire fighting. Due to the continuous circulation; water remains fresh but the losses will be more if there are leakages in the system.
- Intermittent System
If adequate water is not available, the whole community is divided into several zones and water is supplied in each zone for a fixed time in a day or alternate days. The water flows in the consumer’s tap at certain intervals. So, it is called intermittent system.
3.Methods of Water Distribution System
For efficient distribution, it is required that water should reach to every consumer with the required rate of flow. Therefore the same pressure in the pipelines is necessary which should force the water to reach every place. The distribution systems can be classified as follows:
a. Gravity System
When the distribution reservoir is located at a higher elevation than the target community; then water can be supplied with the gravity flow. This method is much suitable when the source is the river or impounded reservoir at sufficient height than the target community. Usually pumping water is not required at any stage of this type of distribution.
Advantage of gravity method
- No energy is required to operate the system as water is conveyed by gravity.
- No pump is required.
Disadvantage of gravity method
- Not applicable in plain or flat terrain like terai where an elevation source of water supply is not available.
- Water loss by leakage is comp[aritively higher as the system remains under constant pressure.
2. Pumping System
In this system, water has to be pumped and then directly send to the public. In the pumping system, a number of pumps are established and only some of them are always used. Some of the other pumps are installed for emergency causes like fire hazards, peak water demand, etc. This method is suitable if the source is not very high than the target community.
However, this system of distribution becomes very expensive for long term use. Also, if electric pumps are used, the water may be insufficient when the power fails. So most commonly diesel pumps are managed for an alternative. This method has no problem with the pressure and maintaining the head at the consumer’s tap.
- Water can be pumped only when required.
- Low water loss due to leakage.
- Break down of system occurs if power fails.
- Maintenance and operation cost is high.
- During pumping hours, the inflow of water through leaks may cause water contamination.
3. Dual System
This method is also called a combination system of gravity and pumping system. The pump is connected to the mains as well as to an elevated reservoir.
In the beginning, when demand is small; water is stored in the elevated reservoir but when demand increases then the flow on the distribution system come from both the pumping station as well as elevated reservoir. As in this water pumps from two sources name from reservoir and pumping system. So it is called the Dual System.
Break Pressure Tank
There is a certain working pressure of pipes and this limit should not be crossed. Due to water flowing in the pipe, hydrostatic pressure is exerted on the joints and fittings of pipe. If this pressure exceeds the allowable working pressure of the pipe, it may burst.
So, to break the hydrostatic pressure, a tank is specially built which is known as a break pressure tank. In this tank, water is permitted to discharge freely in the atmosphere which reduces the hydrostatic pressure to zero. Storage tank, sedimentation tank, collection chamber, distribution chamber, etc will act as a break pressure tank. Break pressure tank are also called break pressure chamber.