Rainwater collection
Estimate collected rainfall, stored water and overflow for a single rain event. Change the inputs to update the chart or diagram.
Your inputs
Values shown are editable examples; verify your own measurements and product specifications. Results update as you edit.
Calculations run in your browser. Inputs are not saved or sent to analytics.
How it works
- Collected water = × × / 100
- Additional water retained = min(Collected water, − )
- Worked example: 100 m² × 20 mm × 80% = 1,600 L; 1,000 L − 200 L = 800 L; Overflow = 800 L
Input and formula key
Your result
Complete the inputs to see your result.
Assumptions and limitations
Rainfall is manually entered in mm, with horizontal projected catchment area in m². One mm over one m² is one litre. Enter your own efficiency including runoff and collection losses; 80% is an example. Model one event with no withdrawals, evaporation or infiltration during it. Initial stored water cannot exceed capacity. No weather feed, drinking-water treatment or tank-sizing reliability model is included.
Sources
- US Department of Energy — rainwater harvesting calculator Sources reviewed: 2026-10-09
