What this tool does
Keeps tariff, active days, sewer-billing treatment, operating cost and installed cost explicit instead of inventing regional prices.
When to use it
Use after a realistic reusable volume is known and after checking the utility's current water, sewer, rebate and billing rules.
Inputs and supported units
Each labelled field explains the quantity it expects. Unit-system changes convert existing numeric entries once and keep calculations on a single SI internal basis. Supported shared units include L/min and GPM, metres and feet, kPa and psi, millimetres and inches, kW and hp, and °C and °F as relevant.
Calculation or decision method
Net savings = avoided water + entered sewer offset − annual operating cost
How to interpret the result
Read the primary result with the supporting breakdown and warning. A plausible number is not evidence that every input, operating case or design constraint has been included.
Worked example
150 L/day for 240 days equals 36 m³/year. At 2.50 water and 3.00 sewer currency/m³ with a 50% sewer offset, gross savings are 144 currency/year before operating cost.
Assumptions
Entered fixture, event, climate, soil and tariff values describe the planning case; volumes are kept on an SI internal basis.
Limitations
The result is a preliminary quantity or cost screen. It does not approve a source, end use, plumbing connection, treatment process, setback, storage time or irrigation method.
Sources
- San Francisco Public Utilities Commission — Graywater Design Manual
- Washington State Department of Health — Greywater Reuse
- U.S. EPA WaterSense — Water Budget Tool
- Australian Government — Australian Guidelines for Water Recycling