Shower Water Calculator Formula

Understand the math behind the shower water calculator. Each variable explained with a worked example.

Use the Shower Water Calculator

Formulas Used

Water per Shower

per_shower = gallons_per_shower

Annual Shower Water

annual_gallons = weekly_gallons * 52

Annual Heating Cost

annual_cost = weekly_gallons * 52 * hot_water_cost

Savings with 1.5 GPM Head

savings_low_flow = (flow_rate - 1.5) * shower_min * showers_per_week * 52 * hot_water_cost

Variables

VariableDescriptionDefault
shower_minShower Duration(minutes)8
flow_rateShowerhead Flow Rate(gal/min)2.5
showers_per_weekShowers per Week7
hot_water_costHot Water Heating Cost(USD/gallon)0.02
gallons_per_showerDerived value= shower_min * flow_ratecalculated
weekly_gallonsDerived value= gallons_per_shower * showers_per_weekcalculated

How It Works

How to Calculate Shower Water Usage

Showers account for about 20% of indoor water use and are a major hot water expense.

Formula

Water per Shower = Duration (min) * Flow Rate (GPM)

Annual Water = Per Shower * Showers/Week * 52

Flow Rates

  • Standard showerhead: 2.5 GPM
  • WaterSense low-flow: 2.0 GPM
  • Ultra low-flow: 1.5 GPM
  • Rain showerhead: 2.0-2.5 GPM

    • Worked Example

    An 8-minute shower with 2.5 GPM showerhead, 7 showers/week, $0.02/gal heating cost.

    shower_min = 8flow_rate = 2.5showers_per_week = 7hot_water_cost = 0.02
    1. 01Water per shower: 8 * 2.5 = 20 gallons
    2. 02Weekly: 20 * 7 = 140 gallons
    3. 03Annual: 140 * 52 = 7,280 gallons
    4. 04Heating cost: 7,280 * $0.02 = $146/year

    Ready to run the numbers?

    Open Shower Water Calculator