http://water.usgs.gov/edu/qa-home-percapita.html 40 gallons http://water.usgs.gov/edu/qa-home-percapita.html 100 gallons a day http://water.usgs.gov/edu/qa-home-percapita.html 100 gallons a day 80 to 100 gallons http://water.usgs.gov/edu/qa-home-percapita.html water facts website consumption 80-100 gallons consumption consumption 80-100 gallons 1/2 gallon in water savings 20 gallons USGS: Water Questions and Answers USGS: Water Questions and Answers two to five gallons per minute estimates 80-100 gallons per day consumption probably 1½ gallons consumption saves 1/8 gallon with each flush consumption http://water.usgs.gov/edu/qa-home-percapita.html consumption 100 gallons a day U.S. Geological Survey Water Science School 100 gallons a day according up to 5 gallons