Interactive Calculator · 2026
Greywater Generation Calculator
Estimate how much greywater — the bath, shower, wash-basin and laundry water — your home generates for reuse. Enter the number of occupants, the greywater each person contributes per day and the share that is worth reusing after treatment.
Daily greywater generated → reusable share after treatment
Your household
People living in the home day to day.
Litres per person per day that end up as greywater — the reusable fraction of daily use from bath, shower and basin, and typically laundry. Excludes toilet and kitchen (blackwater).
Not every litre is recoverable — some is lost to filtration, sludge and system overflow. A well-run greywater setup typically returns 70–90%.
Generated vs reusable greywater
The reusable bar is what a treatment system can realistically hand back to you.
Your home generates roughly 280 litres of greywater a day, of which about 224 litres can be recovered — around 6.72 kL a month diverted from fresh supply.
Reuse needs appropriate treatment and a separate plumbing line. Typical end-uses are garden irrigation and toilet flushing; kitchen and toilet water are usually excluded. See the STP guide library for treatment options.
How this is calculated
- Daily greywater = occupants × greywater per person = 4 × 70 = 280 litres/day.
- Reusable per day = daily greywater × reuse share = 280 × 0.80 = 224 litres/day.
- Monthly reusable = reusable/day × 30 ÷ 1000 = 224 × 30 ÷ 1000 = 6.72 kL/month.
Indicative estimate for concept planning. Greywater must be treated before reuse and carried on a separate plumbing line; confirm the treatment train, storage and end-use against local reuse norms and NBC 2016 Part 9 before you build.
Frequently asked questions
- How does the greywater calculator work?
- It estimates the light-use wastewater your home produces from bath, shower, wash-basin and laundry. It multiplies your number of occupants by the greywater each person contributes per day (LPCD) to get daily greywater, then applies your reuse share to find recoverable litres. Reusable litres times 30, divided by 1,000, gives the monthly reusable volume in kilolitres.
- What values should I enter for occupants, LPCD and reuse share?
- Enter the people who live in the home day to day. Greywater per person typically sits around 40 to 120 LPCD; 70 is a reasonable middle default that counts bath, shower and basin and usually laundry, but excludes toilet and kitchen water. For the reuse share, a well-run treated system usually returns about 70 to 90 percent after filtration, sludge and overflow losses.
- How accurate is this estimate and can I actually reuse the water?
- Treat it as an indicative figure for concept planning, not a design value. Actual greywater varies with fixtures, habits and season. Reuse always needs suitable treatment and a separate plumbing line, and is usually limited to garden irrigation and toilet flushing. Confirm the treatment train, storage and end-use against local reuse norms, NBC 2016 Part 9 and a qualified professional before you build.
Related Guides — Deep-dive reading
Rooftop Water Recycling Integration in Homes: One Non-Potable System from Rain and Greywater
How to combine rooftop rainwater harvesting with greywater and STP reuse into a single non-potable water system — the storage, dual plumbing, controls and seasonal logic that make two sources behave like one reliable supply.
Sewage Treatment PlantsSustainable Plumbing in India: A Whole-Home Water and Energy Strategy
The connector guide to green plumbing for Indian homes — how low-flow fixtures, efficient design, rainwater harvesting, greywater reuse, solar and heat-pump hot water, smarter pumping, leak prevention and durable materials fit together to cut both your water and energy footprint.
PlumbingGreywater Recycling India: Reusing Bathroom Water for Flushing & Gardens
How to recycle the basin and shower greywater from an Indian bathroom — simple diversion versus filtered and disinfected systems, the separate drainage you must plan at construction, storage, dual-plumbing to the WC cistern, and honest numbers on cost, payback and health.
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