Rainwater · Excel workbook
Rainwater Harvesting Potential Calculator
Estimate monthly collection and compare annual potential with demand.
Download free XLSX ↗Version 1.0 · 25 September 2026 · No registration required
What you need
- Catchment area in square metres
- Monthly rainfall in millimetres
- Runoff coefficient and collection efficiency
- Monthly demand in kilolitres
What you get
- Monthly and annual collection potential
- Same-month usable supply and surplus
- Annual demand coverage
How to use it
- Save a working copy and read the instructions in the file.
- Replace illustrative inputs or response fields with your site records.
- Check units, dates and boundaries before using the results.
- Keep the completed file with its supporting evidence.
Method
Collection (kL) = area (m²) × rainfall (mm) × runoff coefficient × collection efficiency ÷ 1,000. Same-month use is limited to demand; no carry-over storage is assumed.
Scope and limitations
Monthly estimates cannot size gutters or final tanks. Storage requires a finer time-step demand balance. Recharge requires hydrogeology and water-quality assessment.
Reference: SWR industrial rainwater guide
Read the related guide: Practical guidance for this tool.