In villages and in some towns where municipal water supply is not available, water is obtained from private wells. In such places, usually the water is pumped up to an elevated storage tank from where the distribution to the building is carried out.
In large towns and cities, municipal water, after due treatment, is available through street mains. If adequate pressure is available, the municipal water can be directly connected to an overhead tank. If the pressure is less, a sump may be provided to collect the water from the municipal supply lime. The capacity of the low-level tank (sump) should be adequate enough to hold water depending on the supply system of the municipal authorities.
Water is pumped from this sump at regular intervals to an overhead tank from where the water is distributed to various parts of the building. In addition to the overhead tank, provision may be made to collect the municipal water directly for drinking and cooking purposes at a convenient place (kitchen) in the building. The water in the overhead tank will take care of other demands.
The capacity of the overhead tank is based on the number of persons using it. It is usually of 200–500 l. If it is more than 5000 l, it is better to average it in a series of interconnected tanks such that they can be easily cleaned. The overhead tanks may be of brick, concrete or readymade PVC tanks. An inlet pipe, on outlet pipe and a drainpipe are connected to each tank.
The underground (or sump) and overhead tanks should be cleaned at regular intervals. They should also be disinfected after cleaning by using chemicals. In some cases separate flushing storage overhead tank is provided exclusively for flushing water closets, etc., as the quantity of water used for this purpose is large and be of low quality. For example, bore well water may be used separately for this purpose. Flushing storage tanks may have the capacities as given in Table 27.1.
Table 27.1 Flushing storage capacities
Design of Water Distribution System
Water distribution system needed for a conventional residential building depends on the following aspects:
- Estimation of water requirement
- Determination of pipe sizes
- Pipe layout principles
1. Estimation of Water Requirement
As per Indian code recommendation (IS: 1172–1983 and SP 57–1993) for residences, 135 l of water per head per day to be used for the design of water supply system. The details of the daily consumption is given Table 27.2.
Table 27.2 Domestic consumption of water
Source: IS: 1172–1983.
The daily consumption will vary depending on the activities in a building. For example, in a hospital with beds, the consumption may be of the order of 340 l per bed per day and for a day school, the consumption will be as low as 45 l per head per day.
2. Determination of Pipe Sizes
In general for a middle class house the average number of pipes needed shall be about 8 and pipes of minimum nominal size of 20 mm diameter are enough. For WCs which are directly connected to overhead tanks, a 25 mm diameter is adequate to get sufficient flow. Minimum recommended size of pipes for different purposes in a building is shown in Table 27.3.
Table 27.3 Recommended sizes of water supply pipes
A thumb rule to assess the size of pipes which can supply two or more branch pipes is as follows (Varghese, 2012):
- Up to 3 numbers of 10 mm branches can be supplied by a 12 mm pipe.
- Up to 3 numbers of 12 mm branches can be supplied by a 20 mm pipe.
- Up to 3 numbers of 20 mm branches can be supplied by a 25 mm pipe.
In order to control the output from overhead tanks, a stop valve or gate valve must be fixed in an accessible place. Apart from control this will help to stop the water supply during repairs.
For multi-storey buildings with many flats, a more complex arrangement of water distribution system should be planned.
3. Pipe Layout Principles
Following rules may be adopted in laying of water supply lines (Varghese, 2012):
- There should not be any cross connection and backflow. Backflow can be eliminated by ensuring the under mentioned conditions.
- Adequate air gap is to be provided between the inlet and final flood level in all places particularly washbasins.
- While connecting cistern to water closet, the inlet and float valve should be suitably fixed.
- Positive pressure at the outlet pipes should always be assured.
- Drainage pipes and water supply pipes should not be laid very close to each other. Especially drainage stoneware pipe which are liable to leak if damaged should not be laid above the water supply line. Further, water supply pipes should not be laid alongside of the pipes carrying foul water.
- Planning of the distribution line should be such that it is accessible for inspection, replacement and repairs. GI pipes should not be buried as they tend to corrode in contact with soils, but they can be laid on walls.
- All pipes including PVC pipes laid inside the building as concealed pipes should be tested for leakage.
Water Supply Fittings and Fixtures
Most of the fittings which are to be used for the water supply are standardised. Some of the fittings which are routinely used in residential water supply are discussed below.
1. Stop Valves
These are fixed in an accessible place for each outlet such as washbasins, water closets, etc., to control and facilitate repair.
2. Gate Valves
These operate as a gate in the pipe. It regulates the flow and when fully open, it offers no resistance to flow. These are used for closing the main pipes from tanks.
3. Ball or Float Valves
These are provided in storage tanks, flushing cistern, etc., to control the level of storage water. The supply is cut off automatically when the water reaches a particular designed level.
4. Bib Taps or Bib Cocks
This is the conventional type of fittings used in washbasins.
5. Pillar Taps
It is the outlet provided from a vertical inlet and horizontal outlet in washbasins in kitchens, lavatories, etc.
6. Self-Closing Taps
They remain open as long as the valve is pressed down and closes when the pressure is released. Such taps are provided in railway stations, hotels, etc.
7. Magnetic Taps
These taps operate as soon as the hand is placed below the tap and closes automatically as soon as the hand is removed. This is a very hygienic tap as one need not to touch the tap to operate. Such taps are provided in airport, hotels and hospitals.
Materials of Water Pipes
Two main types of pipes are Galvanised-iron (GI) pipes and unplasticised Poly-vinyl chloride (UPVC) pipes.
If the quality of water running through the pipe is good, and the pipes are buried GI pipes are excellent. These pipes are available in three grades, viz., A, B and C. Class C is the pipe meant for heavy duty and is cosliest of all. Grade B pipes are generally used for water supply in buildings. In order to identify the type of pipes different colours are used, viz., yellow for grade A, blue for grade B and red for grade C.
UPVC pipes are now-a-days preferred for water supply in buildings. They do not function well when exposed to sunlight. Further the coefficient of expansion of UPVC pipes is about eight times greater than that of GI pipes. UPVC pipes require supports at closer intervals.
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