Inputs
gpm
If you know the flow, enter it here.
gal
Use a container of known volume.
Time how long to fill the container.
gpm
Typical legacy showerheads are around 2.5 gpm.
Thermal & Cost Assumptions
$
$
$
$
$
Results
WaterSense status: —— Calculated flow
— Water per shower
— Annual water
— Annual energy
| Metric | Current | Baseline | Savings |
|---|
WaterSense threshold: ≤ 2.0 gpm (7.6 L/min) indicates high efficiency.
Example Data Table
Click “Load” to apply a row to the input form.
| Label | Units | Flow | Duration (min) | Showers/day | Baseline | Fuel | kWh $ | Therm $ | Water $/kgal | Water $/m³ | Load |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Apartment A | gpm | 1.8 | 7 | 2 | 2.5 | electric | 0.22 | 1.20 | 8.00 | 2.50 | |
| Family Home | L/min | 9.0 | 9 | 3 | 9.5 | gas | 0.18 | 1.10 | 6.00 | 1.80 | |
| Shared Flat | gpm | 2.4 | 6 | 4 | 2.5 | electric | 0.20 | 1.25 | 5.50 | 1.90 |
Formulas Used
- Bucket test flow:
flow = volume / time × 60(units per minute). - Water per shower:
V = flow × duration. - Annual water:
Vy = V × showers/day × days/year. - Thermal energy per liter:
EL (kWh/L) = 0.0011628 × ΔT, whereΔT = Tmixed − Tcold. - Annual energy:
Ey = Vy × EL ÷ efficiency. - Gas conversion:
therms = kWh ÷ 29.300111. - Water cost:
Cost = Vy × rateusing $/m³ or $/kgal as applicable. - Savings: baseline minus current for water, energy, and total costs.
- Payback:
Payback = head cost ÷ annual savings.
How to Use This Calculator
- Choose your preferred units.
- Enter measured flow directly, or use the bucket test.
- Set duration, showers per day, and days per year.
- Adjust baseline flow to compare savings potential.
- Provide temperatures, heater efficiency, and energy pricing.
- Set water pricing to reflect local tariffs.
- Press Calculate, then export results as CSV or PDF.
FAQs
Many efficient heads deliver 1.5–2.0 gpm (≈5.7–7.6 L/min). Lower values typically reduce water and energy without sacrificing comfort for most users.
It’s a practical method. Use a container with known volume and repeat several times for consistency. Average the times to improve accuracy.
Heating demand depends on the temperature rise and heater losses. Including these improves energy and cost estimates for electric or gas systems.
Savings will be near zero. Consider reducing duration, installing a lower‑flow head, or both to meaningfully cut water and energy use.
Yes. Actual flow varies with supply pressure and plumbing restrictions. Measure under typical conditions for the most representative results.
Typical Showerhead Flow Benchmarks
| Class | Flow (gpm) | Flow (L/min) |
|---|
Values are representative; product ratings vary by model and region.
Energy per Liter and Gallon vs Temperature Rise
| ΔT (°C) | kWh per liter | kWh per gallon |
|---|
Computed as 0.0011628 × ΔT kWh/L, before heater efficiency losses.