Calculate shower water and cost
Start with measured flow and shower duration, then add known prices.
Back to calculator ↑Measure flow
Catch water from the showerhead for a timed interval and convert to litres per minute. Pressure and spray mode can change flow from the label.
If a container collects 2 L in 15 seconds, flow is 8 L/min, matching the default. Time the spray mode and pressure actually used. If several showerheads run together, combine their flows or model each use pattern separately.
Separate water and heating
Divide monthly litres by 1,000 to get m³ before multiplying the water rate. Heating energy is litres × temperature rise × 0.001163 kWh/L°C divided by heater efficiency; multiply by the entered electricity rate. Leave unknown prices blank.
Incoming and shower temperatures refer to flowing water, not necessarily the heater setpoint. The 0.001163 factor expresses water’s heat requirement in kWh per litre per °C. The engine divides by entered heater efficiency and assumes every litre is heated to the shower temperature.
Worked default example
At 8 L/min for 10 minutes, one shower uses 80 L. Four household showers a day for 30 days use 9,600 L or 9.6 m³/month. Heating from 25°C to 38°C at 90% efficiency needs about 161.27 kWh. Blank rates leave both cost figures unknown.
At THB 4/kWh, heating costs about THB 645.08. A water rate of THB 20/m³ adds THB 192 for 9.6 m³, giving about THB 837.08 from known rates. Reducing showers from ten to eight minutes cuts modeled water and heating energy by 20%.
Compare with actual bills
Water tariffs can have tiers and fixed charges; water-heating equipment differs in efficiency. Treat this as an incremental estimate from entered rates.
A heat-pump water heater can have a coefficient of performance above one, which does not fit this efficiency field capped at 100%. This model is therefore for heaters described by efficiency up to 100%. Actual bills can also reflect mixing, pipe losses, fixed charges and tiered rates.
Heating energy follows temperature rise. If inlet water is 30°C instead of 25°C while shower temperature remains 38°C, the rise falls from 13°C to 8°C and modeled energy falls in the ratio 8/13 at the same water volume. This separates seasonal inlet temperature from flow and duration effects.
Common questions
Can I enter zero price?
Yes if it truly is zero; otherwise leave it blank.
Is hot-water energy included in water price?
No. Enter heating electricity price per kWh separately; the calculator estimates heating energy from water volume and temperature rise.
What does one minute shorter save?
It saves the measured L/min per shower, multiplied by the number of showers.
Sources and calculation guidance
Check these against your chosen product’s label and instructions.