Sanitation · Understand your wastewater · sanitation-2

Estimate your daily flows

Every treatment system is sized from daily flow. Estimate total wastewater, greywater and a peak-day figure before choosing a system.

How

Start from your water demand estimate in the water module, since most indoor water becomes wastewater.
As a reference, US EPA measured about 50 to 70 US gallons (189 to 265 L) per person per day in older homes and about 40 to 60 gallons (151 to 227 L) in homes with efficient fixtures.
Leaks matter: US EPA found average leakage of about 9.5 gallons (35 L) per person per day, and one running toilet can waste up to 200 gallons a day. Fix leaks before you size anything.
Use the daily flow calculator below. Designers often apply a peaking factor (a Washington State review recommends 2.5) to cover busy days with guests or laundry.
Note that regulators often size septic systems by number of bedrooms, not people (for example Washington State uses 120 gallons per bedroom per day). Ask which method your authority uses.