A storage tank in a water network evens out the difference between a slow, steady source and demand that comes in short peaks, and it gives the pressure that pushes water to the taps. Make it hold at least one full day of the community’s water, so 1,000 L for 20 people at 50 L/day each, put its bottom at least 5 m above the highest tap, and cover it.
Part of Water Distribution
A storage tank holds water between the source and the taps so that supply and demand do not have to match from minute to minute. In a gravity system its height above the taps also sets the pressure.
The Tank Does Three Jobs At Once
It buffers flow. A spring delivers a steady trickle while people draw water in bursts in the morning and evening. The tank fills in the quiet hours and empties at the peaks.
It holds a reserve. If the source falls or a pipe breaks, a day’s water in the tank keeps the community supplied while you fix it.
It makes pressure. Every 10 m of height gives roughly 1 bar, and the tank bottom must be at least 5 m above the highest tap (Tank Placement).
What You Need
- A tank body — a ferrocement tank, masonry, or a food-grade plastic tank
- A place high enough to give the pressure
- A float valve on the inlet (Float Valves)
- An overflow, a drain, a vent and a lid — with insect mesh on the openings
- A pipe to the network from near the bottom, and a way to isolate the tank
Method: Choose, Size, Place, Fit
Step 1: Size it for at least one full day’s demand (Tank Sizing).
Step 2: Choose the place (hillside, tower or other firm site).
Step 3: Build or install it with a firm base, since water is heavy.
Step 4: Fit the float valve, overflow, drain, vent and lid.
Step 5: Clean and disinfect before first use, and clean it at intervals.
Worked Example
20 people × 50 L/day = 1,000 L/day, so a tank of 1,000 L is the minimum. A tank of 2,000-5,000 L gives a comfortable buffer. A 1,000 L tank holds 1,000 kg of water.
Common Mistakes
- Letting the overflow discharge into a drain or a pipe that can fill with dirty water. Keep an air gap between the overflow and anything it runs into.
- No lid. Mosquitoes, animals and dirt get in.
- A tank that cannot be drained or cleaned. Sediment builds up.
- Connecting a second, non-drinking supply to the tank. That is a cross-connection.
Safety
Cleaning the inside of a tank can kill, and the rescuer dies second
A closed or lidded tank can be short of oxygen, and carbon dioxide or hydrogen sulphide can pool at the bottom. The commonest fatality pattern is a second person climbing in after the first collapses. Before anyone goes in, open the tank to the air at two points and ventilate it, put the entrant in a harness tied to a line held by an attendant at the surface, and keep a second person outside whose only job is to pull the line, never to follow. Do not test the air with a flame. A full tank is also a heavy load: 1,000 L is a tonne, so build the base for it.
What’s Next
- Learn next: Tank Sizing — the volume needed for peaks and for emergencies
- Combine with: Reservoir Design — larger storage measured in days of supply