How we supply it: Plastic water tanks are arranged through a partner dealer who quotes, supplies and bills them and pays us a referral commission. If you are building an RCC sump or overhead tank instead, the 20 mm jalli and M-Sand for its concrete come from us, and the TMT from our stock yards.
In one line: A water storage tank holds the house's supply: an underground sump receives municipal or tanker water, and an overhead tank on the terrace feeds the taps by gravity.
How many litres your family needs
Typical estimate: at 135 litres per person per day; garden watering, guests and a washing machine push it up.
An RCC sump 1.5 × 1.2 × 1.2 m inside holds about 2,100 litres.
- Family of 4: 540 L a day, so a 1,000 L overhead tank
- Family of 6: 810 L a day, so 1,000–1,500 L overhead
- 10 people: 1,350 L a day, so 1,500–2,000 L overhead
- Sump for 2–3 days, family of 4: about 1,100–1,600 L, more if supply is irregular
- 5,000 L lasts a family of four about 9 days
Sump and overhead tank: two jobs
A water storage tank holds the house's supply: an underground sump receives municipal or tanker water, and an overhead tank on the terrace feeds the taps by gravity.
The overhead tank's height above the outlets sets the water pressure, about 0.1 bar per metre. Its size sets how often the pump must run.
Tank types
| Type | Where | Note |
|---|---|---|
| Rotomoulded plastic tank (IS 12701) | Terrace, loft | Light, quick to install; multi-layer |
| RCC sump | Below ground | Built with the house; needs waterproof plaster |
| RCC overhead tank | On the terrace structure | Designed with the slab |
| Stainless steel tank | Terrace | No algae; higher cost |
| Underground plastic tank | Below ground | Needs a concrete chamber to resist soil pressure |
Choosing the overhead tank and sump
Plastic overhead tanks are the common choice because they go up on a finished terrace in a day. RCC overhead tanks must be designed and cast with the structure.
For the sump, RCC built with the foundation is the usual choice; underground plastic tanks still need a concrete chamber around them.
Checks on a plastic tank
- The tank should be marked IS 12701 with its capacity and batch.
- Look at the manhole edge: the inner food-grade layer and the UV-stabilised outer layer should both be visible.
- The lid should fit tightly and lock, to keep out mosquitoes and dirt.
- Inlet, outlet, overflow and drain fittings should come with the tank, cleanly threaded.
- The platform must be flat and support the whole base, not a few bricks.
Handling and placing
- Tie tanks down on the terrace before the cyclone season; empty tanks can blow away.
- Keep the lid on and the tank empty until plumbing is complete.
- Wash out the tank and the sump before first use.
Tank mistakes
- A plastic tank set on a few bricks, so its base deforms.
- An overhead tank too low to give the showers usable pressure.
- No overflow pipe or mosquito-proof vent.
- A sump without waterproof plaster, letting groundwater in.
- A sump placed close to the septic tank or soak pit.