Water Demand and Storage Calculator
Work out how much water the site uses in a day and how much to hold in operational storage. Enter each group of occupants with the per-person figure you are using, add process and cleaning water, then choose what the storage covers and for how many days.
What this tool estimates
The daily water demand of the people you enter at the per-person figures you choose, plus the process and cleaning water you add — and the operational storage that covers your chosen part of that demand for the days you set, with fire-fighting water kept out of it.
What it cannot decide
- Which per-person figure is right: it depends on the occupancy, the facilities provided and the norm your authority applies, so it is your input.
- How many days of storage you need — that turns on how reliable the supply is (municipal supply hours, borewell yield, tanker logistics).
- The fire-fighting water storage, which the fire design basis fixes and which is held separately.
- Tank structure and layout, pumps, pipe sizes or water quality.
Result
| Group | People | L/person/day | m³/day | Share |
|---|
| Step | Value |
|---|
| Per-person figures | Domestic | Total demand | Storage |
|---|
Fire-fighting water is not in any figure here. Its volume comes from the fire design basis and the fire authority's requirements, and it is held in its own tank — check the arithmetic with the fire water storage checker. The domestic figure is where the STP hydraulic load starts; process water is not domestic sewage.
Method version 6 October 2026. A screening estimate, not a design: see the limits below.
How this calculator works — and where it stops
What it calculates
The daily water demand of a site — domestic demand from the occupant groups and per-person figures you enter, plus process and cleaning water, each kept on its own line — and the operational storage that holds your chosen part of that demand for the days you set. Fire-fighting water is not part of any figure.
Inputs
- Occupant groups, each with the number of people counted over the day (every shift, plus visitors) and the litres per person per day you are using for that group. No figure is built in: the right one depends on the occupancy, the facilities provided and the norm the authority applies.
- Process water, and cleaning or washdown water with any other daily non-domestic use (landscaping, cooling-tower make-up), in m³/day, KLD or L/day — 0 where there is none.
- What the operational storage covers: total demand, domestic only, or process and cleaning only.
- Days of storage — how long the stored water must carry the site without supply.
- Optional: other storage you justify separately (added once, in m³, kL or L), and operating days per year for an annual figure.
Method
- Domestic demand (m³/day) = Σ people × litres per person per day ÷ 1,000, over every occupant group.
- Process and cleaning water are converted to m³/day (1 KLD = 1 m³/day; 1,000 L = 1 m³) and kept on separate lines.
- Total daily demand = domestic + process + cleaning.
- Operational storage (m³) = the daily demand you chose to cover × days of storage.
- Storage to provide = operational storage + any other storage you entered. A blank is reported as "none entered", never as an assumed figure.
- Annual demand = total daily demand × operating days per year, only when you enter them.
- Sensitivity: every group's per-person figure is moved 20% down and up and the demand and storage recomputed; one more day of storage adds exactly the daily demand covered.
Assumptions
- The per-person figures are yours. Tables such as IS 1172:1993 Table 1 give per-head figures by building type — for factories they differ with whether bathrooms are provided — and NBC 2016 Part 9 Section 1 covers water supply for buildings; a local bye-law, the client's brief or metered use in a comparable building may set a different basis. Check which applies before relying on the result.
- The headcount is people per day, not the most present at one time: a three-shift site counts all three shifts.
- Process and cleaning volumes are daily averages for an operating day; seasonal uses (landscaping, cooling-tower make-up) should be entered for the season that governs.
- Days of storage reflect your judgement of supply continuity — municipal supply hours, borewell yield, tanker reliability. The tool does not recommend a number.
Limitations
- Fire-fighting water is excluded on purpose: its volume comes from the fire design basis and the fire authority's requirements, and it is held in its own tank. Use the fire water storage checker for it.
- Domestic and process water are not mixed: domestic water returns as sewage (the STP's load), process water leaves as effluent with its own treatment route.
- Does not split the volume between an underground sump and an overhead tank, size the transfer pumps or pipes, or say anything about water quality.
- Does not split domestic demand between flushing and other uses. Where flushing is to run on treated water, the split comes from the fixture schedule — and the treated-water reuse savings calculator tests whether it pays.
- Does not check whether the source — municipal connection, borewell permission and yield, tankers — can supply the demand or refill the storage.
Worked example
Produced by running this calculator with the inputs below.
Inputs
- One occupant group: 100 people at 45 L/person/day (a test value, not a standard)
- Process water 2 m³/day; cleaning and washdown 0
- Storage covers total demand, for 1.5 days; no other storage entered
- 300 operating days a year
Working
- Domestic = 100 × 45 ÷ 1,000 = 4.5 m³/day.
- Process and cleaning = 2 + 0 = 2 m³/day.
- Total daily demand = 4.5 + 2 = 6.5 m³/day (6.5 KLD).
- Operational storage = 6.5 m³/day × 1.5 days = 9.75 m³ — 9,750 litres.
- Annual demand = 6.5 × 300 = 1,950 m³.
Result. 6.5 m³/day of demand and 9.75 m³ of operational storage, fire-fighting water excluded; 1,950 m³ a year over 300 operating days.
Sensitivity — what moves the answer
- The per-person figure moves the answer most: 20% lower (36 L) gives 5.6 m³/day and 8.4 m³ of storage; 20% higher (54 L) gives 7.4 m³/day and 11.1 m³. At 30 L instead of 45 L the same site needs 5 m³/day and 7.5 m³.
- Every extra day of storage adds the daily demand it covers: 6.5 m³ here, so 1, 2 and 3 days need 6.5, 13 and 19.5 m³.
- What the storage covers matters as much as how long: storing domestic water only for 1.5 days needs 6.75 m³, against 9.75 m³ for the total.
How engineers use the result
To fix the water balance and the operational tank volumes at concept stage — before the plant room, the terrace load of an overhead tank and the sump excavation are drawn — and to carry a domestic figure into the STP and a process figure into the effluent treatment as separate streams.
When a professional design must replace it
Before tanks are detailed or a supply application is made: a public-health engineer should confirm the per-person figures against the norm the authority applies, the headcount by shift, the process volumes from equipment data, the days of storage against the actual supply arrangement, and the fire-water volume from the fire design — separately.
Sources
- IS 1172:1993 (BIS), Code of Basic Requirements for Water Supply, Drainage and Sanitation — Table 1, Water Requirements for Buildings Other than Residences — per-head figures by building type, which for factories differ with whether bathrooms are provided; its footnote refers fire demand to a separate standard. The tool applies none of these figures — check the edition and table your authority uses
- National Building Code of India 2016 (BIS), Part 9 Plumbing Services — Section 1, Water Supply — the building-code basis for water supply in buildings; confirm the requirement for your occupancy and any local bye-law
Questions people ask before using it
What information do I need before using the water demand calculator?
A headcount for each group of occupants counted over the whole day — every shift, plus visitors — and the litres per person per day you will use for each group, with where that figure comes from: the code table your authority applies, the client's brief or meter readings from a comparable building. Then the process and cleaning water in m³ a day from equipment data or meters, how many days of storage your supply calls for, and any storage you hold for another reason.
Which site conditions change the demand and storage result?
The per-person figure moves the answer most, and it depends on what is provided — bathrooms, a canteen, a hostel or a laundry all raise it. Shift patterns and visitors change the headcount. Process water follows production, and seasonal uses such as landscaping and cooling-tower make-up rise in summer. The days of storage depend on supply continuity: municipal supply hours, borewell yield and how dependable tankers are. Fire-fighting water is a separate volume and does not change this result.
What should I send an engineer for a water demand and storage review?
The water balance — sources, meter readings and what each use consumes — the headcount by shift with the facilities provided, process water by machine or line, the existing tanks with their volumes and locations, the supply arrangement (municipal connection, borewell permission and yield, tankers), and wastewater test data if an STP or reuse is part of the plan.
Optional: ask an engineer to look at it
The result above is yours with no form. If you want an engineer to check it against your drawings, schedules or bills, send a request. Nothing is sent until you press the button.
Request saved
It reached our team with exactly what the preview showed. An engineer will use the number you gave if they need your drawings or data.
Prefer to talk? WhatsApp or the contact form.
Got your number — what next?
A calculator gives you a first figure. These take it further.
The work itself
Read before you specify
- Factory Expansion Water Demand: Domestic, Process, Peaks and Storage
- Why the 3rd Floor Gets a Trickle, the 1st Floor Gets a Jet, and the Pipes Bang at Night
- Rainwater Harvesting for Factories and Commercial Sites
- You're Still Burning Diesel to Heat Water. A Heat Pump Delivers the Same Heat for a Fraction of the Energy.
The terms behind it
Delivered work with this scope
- Full MEPF Package for JMH Prime, Jeewan Mala Hospital — Karol Bagh, New Delhi — Jeewan Mala Hospital
- MEPF for Advantec Wheels Alloy Plant, Jammu — Advantec Wheels
Related calculators
One of 56 free MEPF and solar calculators on this site. Every input term is defined in the engineering glossary; the specification libraries, clearance guides and checklists for design teams are in the architects' section.
Guides that reference this page
- PHE Contractor for a Factory: Scope, Licences and How to Hire One
- MEP Design for a School or College Campus: Phasing, Water and Fire Across Blocks
- Water Treatment for a Factory: Source Quality, RO or Softener, and Cost Drivers
- Solar Module Cleaning for a 1 MW Plant: Water, Frequency, Robots and the Soiling Loss Maths
- Factory Expansion Water Demand: Domestic, Process, Peaks and Storage
- Rainwater Harvesting for Factories and Commercial Sites
Related on this site
- termALMM
- termNet Metering
- termOpen Access (Solar)
- serviceSoil, Waste & Rainwater Drainage (Plumbing)
- servicePumping & Hydro-Pneumatic Systems (Plumbing)
- calculatorMEP Renovation Budget Calculator
- calculatorSolar Open Access Savings Calculator
- buyer's guideHow to Select an MEP Contractor
- guideFactory approvals roadmap, India
- guideCLU for industrial land