How the shower water calculator works
Water use is showers × minutes × flow rate. Heating cost comes from the energy needed to warm the hot share of that water.
Heating energy (kWh) = Gallons × 70% hot × 8.34 lb/gal × 60 °F rise ÷ 3,412 BTU/kWh ÷ 95% efficiency
The calculation assumes about 70% of shower water is hot and that the heater raises it by 60 °F, with an electric resistance heater at 95% efficiency. Heat-pump water heaters use about a third as much electricity, and gas heaters cost a different amount, so treat the heating cost as an electric-heater estimate. Federal rules cap new showerheads at 2.5 GPM, and EPA WaterSense models use 2.0 GPM or less.
Worked example
Three 8-minute showers a day with a 2.5 GPM head use 1,800 gallons a month. Water and sewer at $12 per 1,000 gallons cost $21.60, and electric water heating adds about $33.07, for $54.67 a month. A 1.8 GPM head would save 504 gallons and about $15.31 a month.
Frequently asked questions
How much water does a shower use?
About 2.1 to 2.5 gallons per minute with standard heads, so roughly 17 to 20 gallons for 8 minutes.
Are low-flow showerheads worth it?
Usually yes; they cost little and cut both water and water-heating bills by 20% to 30%.
What is the legal maximum showerhead flow?
2.5 GPM at 80 psi under US federal standards; some states such as California require 1.8 GPM.
Is a bath more water than a shower?
A full bath uses about 35 to 50 gallons, more than a typical short shower.
Updated October 2026. Results are estimates for education, not financial or medical advice. All math runs in your browser; nothing you type is sent anywhere.