Roof catchment yield · Homeowners & designers
Estimate how much rainwater your roof can collect in a year from catchment area, local rainfall and roof runoff coefficient—then size a harvesting tank for your dry-spell demand.
Use your own district rainfall figure
The 1,500 mm default is a rough Kathmandu valley annual average. Pokhara receives far more, and parts of the western Terai and high Himalaya far less. Look up your station's average from the Department of Hydrology and Meteorology before you size a tank.
Your estimate
Roof catchment yield and a storage tank size, from your rainfall, roof surface and household demand.
1,000 sq. ft. of roof plan area
RCC flat slab — the share of rain that reaches the tank
106.6 m³ per year after 10% first-flush loss
Assuming ~80% of annual rain falls across four monsoon months
500 litres/day × 365
Rainwater supplements the mains and tanker supply; it rarely replaces them
10 m³ — 20 days of demand
Length × width × depth for an underground RCC tank, before freeboard
Planning estimate only. Harvested rainwater is not potable without filtration and disinfection. Tank structural design, waterproofing, overflow and recharge arrangements, gutter and downpipe sizing, and any municipal requirement for rainwater harvesting in a building permit are outside this calculation.
What this estimate assumes
Formulas used
Practical guide
Read the related guide for assumptions, ordering tips and ways to compare the estimate with actual site records.
Same-category tools first so each intent stays clustered—then open the full hub if you need a different job.
Frequently asked questions
Yes. The Rainwater Harvesting works in your browser without an account. You can install GharNaksa when you want to track the real project costs, payments and progress.
No. It is a planning estimate based on the information you enter. Verify rates, quantities, drawings, local requirements and contract terms with the appropriate qualified professional before making a commitment.
Use GharNaksa to record actual material deliveries, labor, payments, bills and site photos. Comparing the estimate with a dated site record helps reveal cost differences early.