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Most Indian homes have undersized water tanks because no one calculated the actual requirement. IS 1172:1993 gives you an LPCD formula — and the answer will likely surprise you.
Most Indian homeowners size their water storage by intuition — "one tank should be enough" — and add more later when the shortage becomes obvious. This approach is expensive (retrofitting tanks means structural work on the terrace) and avoidable.
IS 1172:1993 — the Code of Basic Requirements for Water Supply, Drainage and Sanitation — specifies the minimum water requirement per person per day for every type of use. These are the numbers your plumbing designer should be starting from.
IS 1172:1993 Table 1 specifies the following design requirements:
| Type of Building | LPCD Requirement |
|---|---|
| Residential (with flush toilets) | 135 LPCD |
| Residential (with waterborne sewage) | 200 LPCD |
| Hotel / Guest House | 180 LPCD |
| School (day) | 45 LPCD |
| Office / Commercial | 45 LPCD |
For a standard residential building with flush toilets, IS 1172 requires 135 litres per person per day as the design basis. A family of four therefore needs 540 litres per day minimum.
Step 1: Calculate daily requirement using IS 1172.
Step 2: Determine your municipal supply frequency. If water comes once every 48 hours, you need 2 days of storage.
Step 3: Add an overhead tank for gravity distribution.
Step 4: Account for peak demand. IS 1172 uses a peak factor of 1.8 for domestic supply — meaning the peak hour demand is 1.8 times the average hourly demand. Your pump and pipe sizing must accommodate this.
1. Treating IS 1172 as optional. Many plumbers size by habit ("two 1,000L tanks always works") without calculating. In a 6-bedroom house with three bathrooms, two 1,000L tanks may cover only 12 hours of supply interruption.
2. Ignoring servant quarters and guard rooms. IS 1172 counts every person on the premises. If you have live-in domestic staff, add 135 LPCD per person.
3. Not accounting for garden or car-washing. IS 1172 does not cover landscape irrigation — you need to add this separately based on garden area.
4. Under-specifying the sump pump. The pump must refill the overhead tank within 2–3 hours of the municipal supply window. Undersizing the pump makes the full tank capacity useless.
Once you know daily requirement, IS 1172 helps you size pipe diameters too. The main rising main from sump to overhead tank should carry the full daily refill in 2 hours — which determines the pipe diameter and pump head requirement.
NirmanShastra's PlumbingPro tool takes your family size, floor count, and municipal supply schedule, applies IS 1172:1993 norms, and produces a complete plumbing schedule with tank sizes, pipe diameters, and fixture counts.
*Size your water storage correctly from day one — try PlumbingPro for an IS 1172:1993 compliant plumbing estimate.*