Cut demand first, before sizing anything
Every litre you do not use is a litre you do not need to collect, pump, treat or store. Conservation is the cheapest water source an off-grid estate has.
How
- Choose efficient fixtures. US EPA WaterSense labels water-efficient toilets, showerheads, taps and appliances, and offers a calculator to estimate savings.
- Consider a dry or composting toilet (see the sanitation module) to remove the toilet line from the budget entirely.
- Plan greywater reuse for the garden with the sanitation module, so shower and laundry water does double duty.
- Use rainwater or other non-potable water for toilets, laundry and garden where your local code allows, and keep full treatment for the potable line only.
- Mulch and drip-irrigate the garden (food module) instead of spraying.
- Re-run the budget with these changes. Use the new conserving figure for all sizing, and keep the comfortable figure as the upper case.
Do these first
Sources
- How We Use Water. US EPA WaterSense, accessed 2026-11
- The Texas Manual on Rainwater Harvesting, 3rd edition. Texas Water Development Board, accessed 2026-11
- Collecting Rainwater and Your Health: An Overview. US Centers for Disease Control and Prevention (CDC), accessed 2026-11