Build a household water demand budget
Before you look for water, work out how much you need per day in litres. Every later decision (source, tank size, pump, treatment flow) is sized from this number.
How
- List everyone who will live on the estate, plus regular guests.
- Start with the humanitarian floor. Sphere sets 2.5 to 3 L per person per day for drinking and food. It sets at least 15 L for drinking, cooking and hygiene. Treat this as your emergency minimum, not your comfort level.
- Sphere calls 15 L a survival level. It targets up to 20 L per person per day in extreme climates, with many medical needs or when cooking uses a lot of water.
- WHO Technical Note 9 gives the same picture: about 7 L per person per day (3 to 4 L drinking plus 2 to 3 L food preparation) keeps people alive for only a few days, and 15 to 20 L covers drinking, cooking, personal hygiene and laundry for a few months.
- Estimate normal indoor use. The Texas rainwater manual puts a water-conserving household at about 95 to 190 L (25 to 50 US gallons) per person per day indoors. New York State uses about 416 L (110 US gallons) per bedroom per day for moderate use when sizing wells.
- Record three figures per person: emergency minimum, conserving target and comfortable use. Multiply by the number of people.
- Write the budget as a table with one line per use (drinking and cooking, showers, toilets, laundry, cleaning), so you can see what to cut in the next steps.
- Keep potable (drinking quality) and non-potable lines separate in the table. Only drinking, cooking, teeth brushing and washing food truly need full treatment, which shapes the treatment and plumbing design later.
Do these first
Sources
- Sphere Handbook, Water supply standard 1: access and water quantity (interactive edition). Sphere Association, accessed 2026-11
- The Texas Manual on Rainwater Harvesting, 3rd edition. Texas Water Development Board, accessed 2026-11
- Individual Water Supply Wells: Fact Sheet #2 (yield and storage). New York State Department of Health, accessed 2026-11
- Technical Note No. 9: Minimum water quantity needed for domestic uses (WHO/SEARO, hosted copy). World Health Organization (hosted by Medbox), accessed 2026-11