🔧 Plumbing

Water Supply Pipe Calculator

Calculate water supply pipe sizes for residential and commercial buildings. Determine daily demand, storage capacity, and pipe diameters per NBC 2016.

📐 Standard: NBC 2016 Part 9 / IS 1172
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Water Supply Pipe Calculator Calculator
Reference: NBC 2016 Part 9 / IS 1172
🔧 Plumbing
Calculate water supply pipe sizes for residential and commercial buildings. Determine daily demand, storage capacity, and pipe diameters per NBC 2016.
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ℹ️ About This Calculator

The water supply pipe calculator starts from occupancy-based demand (litres per person per day) to determine daily water demand, storage tank capacity, and the required pipe sizes for the rising main and distribution network. Based on NBC 2016 Part 9 (Plumbing Services) and IS 1172 (Basic Requirements for Water Supply and Drainage).

NBC 2016 Part 9 is the primary reference for plumbing design in Indian buildings. Two-tank system (underground sump + overhead tank) is standard across India due to intermittent municipal supply. Rising main pump transfers from sump to overhead tank. Pressure zones required for buildings above 6 floors. Backflow prevention: double check valves at all connections to mains. Water meters: mandatory for buildings consuming > 500 KLD.

📐 Water Demand and Pipe Sizing

NBC 2016 Part 9 / IS 1172

Daily Demand (NBC 2016):
  Residential: 135 L/person/day (basic); 150–200 L for higher income
  Office: 45 L/person/day (including canteen)
  Hospital: 340–450 L/bed/day (clinical use)
  Hotel: 180–250 L/guest/day

Storage Tank:
  V_tank ≥ 2 × daily demand (2-day storage for overhead)
  Underground sump: V_sump ≥ daily demand

Rising Main Flow:
  Q_main = V_tank / fill_time (typically 4–6 hours)
  Pipe sized for Q_main at velocity ≤ 2.5 m/s

🧮 Worked Example

A residential apartment building has 120 occupants at 150 L/person/day, giving a daily demand of 120 × 150 = 18,000 litres (18 kL). Following the 2-day storage rule, the overhead tank is sized at 18 kL and the underground sump at 18 kL. The overhead tank is filled from the sump in 4 hours, so the rising main flow is Q = 18,000/4/60 = 75 L/min (1.25 L/s). At a limiting velocity of 2.5 m/s, this flow requires a rising main of approximately 32 mm nominal diameter, with a transfer pump sized for this flow plus the total static and friction head.

❓ Frequently Asked Questions

How large should the overhead water storage tank be? +
NBC 2016 minimum: 1 day's water demand for overhead tank + 1 day's demand for underground sump (total 2 days' storage). For areas with unreliable supply (many Indian cities): 2–3 days' storage in the sump is advisable. For residential buildings: plan 150–200 L per person per day. A 20-flat building with 100 persons needs 15,000–20,000 litres = 15–20 kL overhead tank minimum.
What is the two-tank system and why is it used in India? +
Municipal water supply in most Indian cities is intermittent (1–4 hours/day at low pressure). The two-tank system stores water: underground sump (large volume) collects municipal supply whenever available; pump transfers to overhead tank continuously or on timer; gravity feed from overhead tank to all fixtures. This ensures 24/7 water availability regardless of municipal supply timing.
What pump is needed to fill the overhead tank? +
Rising main pump (transfer pump): flow rate = V_overhead / fill_time. If overhead tank = 20 kL and fill time = 4 hours: Q = 20,000/4/60 = 83 L/min = 1.4 L/s. Head = static height (building height + overhead tank height above roof) + pipe friction + 5 m residual. A typical residential building: 30–50 m total head, 1–3 L/s flow = 1.5–3 kW pump.
What water pressure is required at plumbing fixtures? +
Minimum residual pressure: 1.0 bar (10 m head) at flush valves, 0.7 bar (7 m) at showers and basin taps. Maximum: 3.5 bar (35 m) to prevent fixture damage and water hammer. Buildings above 6–7 floors need pressure zones or pressure reducing valves (PRVs) at each zone to keep pressure within 1–3.5 bar range. Gravity from a 10 m high overhead tank gives approximately 1 bar at the connection point.
Do rainwater harvesting systems need to be integrated with the water supply? +
NBC 2016 and most State building codes require rainwater harvesting (RWH) for buildings over a certain footprint (varies by state). The harvested rainwater is typically stored in the sump and used for flushing, gardening, and groundwater recharge. RWH and potable water must be completely separated – no cross-connection. RWH water needs treatment (filtration + disinfection) before use for potable purposes.

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