Place the storage tank so its bottom is at least 5 m above the highest tap in the system, because every 10 m of height gives about 1 bar and a tap needs 0.5 bar at least. A tank whose bottom is 22 m above the lowest tap and 7 m above the highest gives about 2.2-2.4 bar at the lowest and 0.7-0.9 bar at the highest before friction losses, which leaves 2 m of head for friction.
Part of Water Distribution
Tank placement is choosing the height and the site of a distribution tank so that every tap receives enough pressure without any pipe seeing too much. The pressure comes from the height of the water surface above the tap, not from the tank’s size.
Height Is What Matters, Not Volume
A 100 L tank and a 5,000 L tank at the same height give the same pressure at a tap. The pressure at a tap is the vertical distance from the water surface in the tank down to the tap: roughly 1 bar for every 10 m (a metre of height gives about 0.1 bar). So the tank has to be high enough to serve the highest tap and low enough that the lowest tap does not see more than 6 bar.
The minimum comes from the 5 m (0.5 bar) at the highest tap. The tank’s height matters too: the tank is fullest at its highest water level, which is the bottom plus the water depth, and emptiest at the bottom. The pressure at a tap swings between those two.
Where To Put It
- A hillside above the settlement, using the terrain; pipe from the source to the tank, then from the tank to the buildings below.
- A tower tank: a platform or tower that lifts a tank above the settlement, for example a 3 m tower with a 2 m tall tank, which puts taps 3-5 m below the tank bottom (Gravity-Fed Water & Plumbing Systems).
- A roof: simple but needs a strong roof, since 1,000 L is 1,000 kg.
What You Need
- Heights of every tap and candidate tank site, from a level survey
- The tank depth when full
- A firm, stable site on solid ground, not on fill or a slope that could slide
- An overflow route that does not run toward houses
Method: Check Both Ends
Step 1: Measure the height of the tank bottom above the highest tap.
Step 2: Check it is at least 5 m, plus the friction allowance for the run.
Step 3: Measure the height above the lowest tap, and add the tank depth for the full-tank case.
Step 4: Check that figure is under 60 m. If not, use a break pressure tank or pressure zones.
Worked Example
Tank bottom 22 m above the lowest tap and 7 m above the highest, tank 2 m tall:
- Lowest tap: 22 m (tank empty) to 24 m (tank full) of head = 2.2-2.4 bar
- Highest tap: 7 m (empty) to 9 m (full) = 0.7-0.9 bar, before friction
The minimum is 5 m, so the allowance for friction is 7 − 5 = 2 m with the tank at its lowest level. The run to that tap must lose no more than 2 m, which can be checked with Pipe Sizing. If it loses more, raise the tank or use a larger pipe.
Common Mistakes
- Counting from the tank top. The tank is only that full part of the time; use the bottom.
- Ignoring friction. The 5 m is at the tap while water is flowing.
- Putting the tank where it can slide or collapse. Full, it weighs tonnes.
- Placing a big tank directly above houses with no overflow route. If it fails, the water goes downhill.
Safety
A full tank is a heavy, falling load
A 5,000 L tank holds 5 tonnes of water, and a failed tank or stand releases it all at once. Build the base for the full weight, keep tanks off unstable slopes, and do not build homes or work areas directly downhill of a large tank without an overflow and failure route that leads away from them.
What’s Next
- Learn next: Tank Sizing — how big the tank should be
- Combine with: Float Valves — keeping the level automatic