Free water usage and cost calculator

How to use

1. Enter the number of people in your household.
2. Fill in your daily shower habits and bath frequency.
3. Enter toilet flushes per day per person, dishwasher loads, and laundry loads per week.
4. Add outdoor watering gallons per day if applicable.
5. Set your water rate per gallon and click Calculate.

Formulas

showerGal/day = showersPerDay × showerMinutes × 2 gal/min
bathGal/day   = bathsPerWeek × 36 gal ÷ 7
toiletGal/day = flushesPerDayPerPerson × people × 1.6 gal
dishwasherGal/day = loadsPerWeek × 4 gal ÷ 7
laundryGal/day    = loadsPerWeek × 20 gal ÷ 7
totalDailyGal = sum of above + outdoorGal
monthlyGal    = totalDailyGal × 30.44
monthlyCost   = monthlyGal × pricePerGallon

Worked example

3-person household, default settings, $0.004/gal:

Monthly: 74.5 × 30.44 ≈ 2,267 gallons
Monthly cost: 2,267 × $0.004 ≈ $9.07

Notes

• Rates are based on EPA WaterSense and ENERGY STAR standards for modern fixtures.
• Older toilets (pre-1994) use 3.5–7 gallons per flush — significantly more than the 1.6-gallon low-flow standard.
• Standard (non-HE) washing machines use 40+ gallons per load versus 15–25 for HE models.
• Outdoor watering varies enormously — a single sprinkler zone runs 15–30 gallons per minute.