💧 PLUMBING

Water Storage Tank Calculator (Sump & Overhead)

Calculate sump tank and overhead water tank capacity from building type and occupancy. IS 1172 and NBC Part 9 compliant. Free tool.

📐 Standard: IS 1172 / NBC Part 9
✅ Free to use
📄 PDF export
📱 Mobile friendly

ℹ️ About This Calculator

Every building requires adequately sized water storage to handle supply interruptions and peak demand periods. IS 1172 (Code of Basic Requirements for Water Supply) specifies the minimum daily water demand per capita for different building types. NBC Part 9 requires a minimum storage of 24 hours of total daily demand between the underground sump and overhead tank.

NBC 2016 Part 9 mandates that the sump and overhead tank together store a minimum of 24 hours of total building demand. In areas with unreliable supply (common in many Indian cities), engineers typically design for 48 hours of storage. The overhead tank must be located at sufficient height to maintain minimum 7m head at the lowest floor water outlet. Pumping is required from sump to overhead tank — size the pump for the total static head plus friction loss in the rising main.

📐 Tank Sizing Formula (IS 1172 / NBC Part 9)

IS 1172 / NBC Part 9

Daily Demand:
  Q_daily = N × LPCD (litres per capita per day)

IS 1172 LPCD values:
  Residential (piped supply): 135 L/person/day
  Residential (flushing + bathing): 200 L/person/day
  Commercial office: 45 L/person/day
  Hotel: 180 L/room/day
  Hospital: 450 L/bed/day
  School (day): 45 L/student/day

Storage Split (NBC Part 9):
  Underground sump: 2/3 of daily demand
  Overhead tank:    1/3 of daily demand
  Fire reserve:     As per NBC Part 4 (separate from domestic)

❓ Frequently Asked Questions

How do I calculate the water tank size for an apartment building? +
Multiply the number of residents by 135 L/person/day (IS 1172 piped supply norm). For a 100-person apartment: 100 × 135 = 13,500 L/day = 13.5 KL/day. Provide 2/3 in the underground sump (9 KL) and 1/3 in the overhead tank (4.5 KL). Add fire reserve separately as required by NBC Part 4.
What is the standard LPCD for different building types in India? +
IS 1172 provides: Residences (cities) — 135 L/capita/day minimum, 200 L recommended. Schools — 45 L/student. Offices — 45 L/person. Hotels — 180 L/room. Hospitals — 450 L/bed. Factories — 30–45 L/worker. Restaurants — 70 L/seat. These are minimum standards; actual consumption in Indian cities is often 150–250 LPCD.
Should the fire water tank be separate from the domestic water tank? +
Yes — NBC Part 9 and NBC Part 4 require the fire water reserve to be stored separately from the domestic supply in a dedicated fire water tank or a clearly demarcated section of the sump. Fire water must be exclusive to fire fighting use and must not be drawn for domestic purposes. The fire reserve is additional to the 24-hour domestic storage.
What height should the overhead tank be placed at? +
The bottom of the overhead tank should be at sufficient height to provide minimum 7m static head at the topmost water outlet. For a multi-storey building, the tank goes on the roof — ensure the structural slab can carry the weight (water: 1 kg/litre, so 10 KL = 10,000 kg = 100 kN). Always engage a structural engineer for overhead tank support design.
What material should be used for water storage tanks in India? +
IS 12701 and IS 2049 specify requirements. Approved materials: food-grade HDPE tanks (IS 12701), RCC tanks with cement mortar lining, stainless steel (SS 304/316), FRP/GRP. Avoid galvanized iron tanks for drinking water storage. For large capacities (>50 KL), RCC underground sumps are most cost-effective. For rooftop overhead tanks, HDPE or SS tanks are standard.

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⚠️ Disclaimer: For preliminary engineering design only. Verify all results with a licensed engineer before use. Full disclaimer →

💧 Water Storage Tank Calculator
Reference: IS 1172 / NBC Part 9