Compare two showerheads to estimate yearly water and bill savings, then see how long a rebate-adjusted purchase price takes to recover.
Advanced options
Table of contents
How to use our Low-Flow Showerhead Savings Calculator
- Enter the flow shown on your current and replacement showerhead labels in GPM, plus your usual Minutes per shower.
- Enter Household showers per day for everyone using the shower and your combined Water and sewer rate from a utility bill.
- Open Advanced options if you want to include a heating estimate, Replacement showerhead price, or Utility rebate.
- Select Calculate, then compare Yearly water saved with Yearly combined bill savings and Simple payback time.
- Sanity-check the result: if the Replacement showerhead flow is lower than the Current showerhead flow, Yearly water saved and Shower water reduction should be positive when shower habits stay the same.
Definitions
GPM: Gallons per minute, the flow rate of water from a showerhead.
Water and sewer rate: The amount charged for 1,000 gallons of water use, including variable sewer charges when they are tied to water use.
Heated-water share: The percentage of saved water that came from the water heater.
Water-heating cost: Your estimated energy cost to heat one gallon of water.
Net replacement price after rebate: Replacement showerhead price minus Utility rebate. A negative amount means the entered rebate is larger than the price.
Simple payback time: Estimated months of combined bill savings needed to equal the net replacement price.
Shower water reduction: The percentage difference between the current and replacement flow rates, assuming the shower length stays the same.
Common mistakes and quick fixes
Mistake: Entering the showerhead flow in gallons per hour instead of Current showerhead flow in GPM.
Fix: Use the GPM number printed on the showerhead or its product information.
Mistake: Entering one person's showers in Household showers per day when several people use the shower.
Fix: Add the household's average daily showers before calculating.
Mistake: Using only the water charge in Water and sewer rate when sewer charges also rise with water use.
Fix: Add the variable water and sewer charges and enter the total per 1,000 gallons.
Mistake: Treating Share of saved water that was heated as the share of the whole shower.
Fix: Enter the percentage of the water saved that your water heater supplied; leave it at 0 if you do not have an estimate.
Mistake: Entering a promised but unconfirmed incentive as Utility rebate.
Fix: Enter only a rebate you expect to receive, since it lowers Net replacement price after rebate.
Mistake: Assuming a negative Shower water reduction is a savings.
Fix: A negative percentage means the Replacement showerhead flow is higher and is estimated to use more water.
Limitations & Key Assumptions / Boundary Conditions
- The yearly estimate uses 365 days and assumes Minutes per shower and Household showers per day stay the same all year.
- The comparison uses the listed flow rates. Actual flow can differ because of water pressure, plumbing, a flow restrictor, or showerhead condition.
- Water and sewer savings depend on the Water and sewer rate entered. Fixed utility charges are not included because they do not change with gallons used.
- Water-heating savings use your entered Share of saved water that was heated and Water-heating cost. They do not model water temperature, heater efficiency, fuel type, standby losses, or local energy prices.
- Simple payback includes only the entered Replacement showerhead price and Utility rebate. It excludes installation, sales tax, maintenance, financing, and future rate changes.
- If the replacement flow is higher than the current flow, water and bill savings can be negative. In that case, a positive purchase price does not have a meaningful savings payback.
Methodology
Calculation method
The calculator first finds the gallons avoided in one year from the difference in showerhead flow, shower length, and household shower frequency.
Yearly water saved = (Current showerhead flow - Replacement showerhead flow) x Minutes per shower x Household showers per day x 365
The entered Water and sewer rate is priced per 1,000 gallons, so yearly gallons are divided by 1,000 before applying the rate.
Yearly water and sewer savings = Yearly water saved x Water and sewer rate / 1,000
Water-heating savings apply only to the portion of saved water entered as heated water.
Yearly water-heating savings = Yearly water saved x (Share of saved water that was heated / 100) x Water-heating cost
Yearly combined bill savings = Yearly water and sewer savings + Yearly water-heating savings
The purchase amount remains signed after subtracting the rebate.
Net replacement price after rebate = Replacement showerhead price - Utility rebate
Simple payback time = 12 x Net replacement price after rebate / Yearly combined bill savings
Shower water reduction = 100 x (Current showerhead flow - Replacement showerhead flow) / Current showerhead flow
Mini-example
For a change from 2.5 GPM to 1.8 GPM, 8-minute showers, and 2 household showers per day, yearly water saved is (2.5 - 1.8) x 8 x 2 x 365 = 4,088 gallons. At $10 per 1,000 gallons, yearly water and sewer savings are $40.88 before any heating estimate. A $30 showerhead with no rebate has a simple payback of about 8.8 months if combined yearly savings are $40.88.
Calculation choices
Blank advanced entries count as $0 or 0 percent. The calculator keeps negative water and bill savings when the replacement has a higher flow rate, so the comparison does not hide added use. Payback is not available when Yearly combined bill savings equal $0, and Shower water reduction cannot be calculated when Current showerhead flow is 0 GPM.