Water budget
Daily water use by fixture, garden and animals. Learn the ideas behind it in Lesson 20: Project: my water budget.
Planning tool
Estimate a day of water use by fixture. Efficient fixtures and habits shrink everything downstream: tank, pump, treatment and greywater.
Older toilets use 3.5 or more. WaterSense models use 1.28 or less.
Standard heads use 2.5; WaterSense heads 2.0 or less.
Efficient front-loaders use about 15 to 20; older top-loaders 30 to 40.
Check your state's greywater rules first (Lesson 19).
About 92 gallons a day (348 L) in peak summer
Indoors: 81 gal/day, or 41 gal per person. That is about 2,437 gallons a month.
A planning estimate, not a design. Take it to a qualified professional before you buy or build.