Impact Tech Solutions · HSE Calculators
Water Consumption / Discharge Calculator
Formula Reference — Return-to-Sewer Method
Water Supply Cost = Water Consumption × Water RateDischarge Volume = Water Consumption × Return-to-Sewer %
Sewerage Cost = Discharge Volume × Sewerage Rate
Total Cost = Water Supply Cost + Sewerage Cost
This is the standard utility billing methodology used by most municipal/industrial water authorities: since discharge volume is rarely metered directly, it's estimated as a percentage of metered supply (the "return-to-sewer" or "consumptive loss" factor), accounting for water lost to evaporation, product incorporation, irrigation, or other non-discharged uses.
Methodology, interpretation & sources
Purpose. Calculates combined water supply and sewerage/discharge cost using the standard return-to-sewer billing method.
How to use the result. Start with source data you can verify, enter values on a consistent unit and time basis, and record the assumptions used. The main inputs on this page include Water Consumption (m³/month), Water Supply Rate ($/m³), Return-to-Sewer Percentage (%) Portion of supplied water assumed to be discharged as wastewater (commonly 80-95% for typical facilities; less for processes with high evaporation/consumption)., Sewerage/Discharge Rate ($/m³), Your Name, Email. Re-run the calculation when those assumptions change rather than carrying an old result forward.
Decision use. Use this result for environmental planning and internal tracking, then verify reporting boundaries, factors and units against the framework used for your formal disclosure or permit.
Limitations. Emission factors, conversion factors, system boundaries and local permit conditions can change the reported result.
Primary references. Use the current edition/version that applies to your jurisdiction and organization:
Editorial note. Prepared and maintained by Impact Tech Solutions. Editorially updated 28 September 2026. No individual professional credential is claimed on this page; high-consequence, statutory, tax, engineering or health decisions should be independently verified against the current primary source and, where required, a qualified professional.
Verification checklist before relying on this result
- Confirm the source and date of Water Consumption (m³/month), Water Supply Rate ($/m³), Return-to-Sewer Percentage (%) Portion of supplied water assumed to be discharged as wastewater (commonly 80-95% for typical facilities; less for processes with high evaporation/consumption)., Sewerage/Discharge Rate ($/m³), Your Name and keep units consistent.
- Check that zero, blank, percentage and currency entries mean what the calculator expects; do not use a placeholder value as real data.
- Repeat the calculation with a plausible low and high assumption to see whether the decision changes materially.
- Record the result together with the assumptions, not as a stand-alone number.
- For statutory, tax, engineering, health or safety decisions, compare the output with the current primary requirement and obtain competent review where required.
A calculator is most useful when it makes assumptions visible. If a small input change produces a very different outcome, treat that sensitivity as part of the decision rather than selecting only the most favorable result.