छानाबाट कति पानी आउला?Turn local rain into a usable estimate

तपाईंको छानाबाट कति वर्षाको पानी संकलन हुन्छ?How much rainwater can you harvest from your roof?

छानाको footprint, आफ्नो ठाउँको वर्षा र संकलन दक्षता राख्नुहोस्। ट्याङ्कीमा पुग्न सक्ने पानीको अनुमान देखिन्छ।Enter the roof footprint, rainfall for your location and period, and collection efficiency. The calculator estimates water that could reach your tank.

छाना, वर्षा र प्रयोगRoof, rainfall, and use

पानी आउने छानाको footprintRoof footprint draining to tank

m²

Gutter मा जोडिएको भागको माथिबाट देखिने area प्रयोग गर्नुहोस्, ढल्केको surface area होइन।Use the overhead footprint that drains to the gutters, not the sloped roof-surface area.

छानिएको अवधिको स्थानीय वर्षाLocal rainfall for the chosen period

DHM को नजिकको station वा आफ्नै rain gauge को उही महिना वा अवधिको कुल राख्नुहोस्।Use the same month or period total from a nearby DHM station or your own rain gauge.

संकलन दक्षताCollection efficiency

80% नेपाल सरकारको उदाहरण हो। Roof material, first flush, gutter overflow र चुहावटअनुसार बदल्नुहोस्।80% follows the Nepal government example. Change it for roof material, first flush, gutter overflow, and leaks.

तपाईंको ट्याङ्की क्षमताYour tank capacity

यसले tankfuls मात्र देखाउँछ। Overflow वा tank size निकाल्दैन।This shows equivalent tankfuls only. It does not calculate overflow or tank size.

तुलनाका लागि दैनिक पानी चाहिने मात्राDaily water need for comparison

L/day

400 L नमुना मात्र हो। Meter वा आफ्नै प्रयोगअनुसार बदल्नुहोस्।400 L is an editable example. Replace it with metered or observed use.

संकलन हुन सक्ने पानीPotential harvest

ट्याङ्कीसम्म पुग्न सक्नेEstimated harvestable water36,000 Lछानिएको वर्षा अवधिमाfor the entered rainfall period

छानामा परेको जम्मा पानीRain falling on roof45,000 L

अनुमानित नोक्सानीEstimated collection loss9,000 L

ट्याङ्की बराबरEquivalent tankfuls12.0

प्रयोग बराबरEquivalent supply90.0 days

यो पानी उपलब्ध हुने guarantee होइनThis is not a water-supply guarantee

वर्षा कहिले र कति जोडले पर्छ, tank पहिले कति भरिएको छ, बीचमा पानी कति चल्छ र overflow कति हुन्छ भन्ने यसले model गर्दैन। पिउने पानीका लागि सुरक्षित catchment, first flush, filter, उपचार र नियमित जाँच चाहिन्छ।This does not model rainfall timing and intensity, starting tank level, water drawn between storms, or overflow. Drinking-water use needs a safe catchment, first flush, filtration, treatment, and routine inspection.

हिसाब कसरी हुन्छ?How the calculation works

1 mm वर्षा 1 m² छानामा पर्दा 1 litre पानी हुन्छ। त्यसबाट first flush, evaporation, splash, gutter overflow र leak को असर efficiency ले घटाइन्छ।One millimetre of rain over one square metre equals one litre. Collection efficiency then accounts for first flush, evaporation, splash, gutter overflow, and leaks.

gross litres = roof footprint m² × rainfall mm
harvestable litres = gross litres × collection efficiency %
estimated loss = gross litres − harvestable litres
equivalent tankfuls = harvestable litres ÷ tank capacity
equivalent supply days = harvestable litres ÷ entered daily need

Tankfuls र supply days volume तुलना मात्र हुन्। सही storage design का लागि कम्तीमा monthly rainfall, monthly demand, tank balance र लामो सुख्खा अवधि जाँच्नुपर्छ।Tankfuls and supply days are volume comparisons only. Storage design needs at least monthly rainfall, monthly demand, a tank balance, and the longest dry period.

काठमाडौंको नमुना हिसाबWorked Kathmandu example

नेपाल सरकारको training material मा July का लागि 100 m² छाना, 450 mm वर्षा र 80% संकलनको उदाहरण छ। तुलना गर्न 3,000 L ट्याङ्की र 400 L/day प्रयोग राखिएको छ।A Nepal government training example uses a 100 m² roof, 450 mm of July rainfall, and 80% collection. A 3,000 L tank and 400 L/day demand are added only for comparison.

100 × 450 = 45,000 Lछानामा परेको पानीrain falling on the roof

45,000 × 80% = 36,000 Lसंकलन हुन सक्नेpotential harvest

36,000 ÷ 3,000 = 12.0ट्याङ्की बराबरequivalent tankfuls

36,000 ÷ 400 = 90.0 daysयदि सबै पानी सुरक्षित राखेर प्रयोग गर्न सकियो भनेonly if all water can be safely stored and used

स्रोत र मान्यताSources and assumptions

Government of Nepal, Ministry of Federal Affairs and General Administration, rainwater-harvesting training material, checked 31 Aug 2026. Its Kathmandu example calculates 100 m² × 0.45 m × 80% = 36 m³, or 36,000 litres.
WHO, Sanitary Inspection Packages: Rainwater Collection and Storage, 2024, checked 31 Aug 2026. WHO gives annual collection as rainfall in mm × roof area in m² × a runoff coefficient and explains that the coefficient accounts for system losses.
Nepal Department of Hydrology and Meteorology, Monthly Climate Reports, checked 7 Sep 2026. Use rainfall for the nearest relevant station and the same period being estimated.
Texas Water Development Board, The Texas Manual on Rainwater Harvesting, checked 31 Aug 2026. It defines catchment area as the roof footprint and explains why storage sizing needs rainfall timing, demand, and dry-period analysis.

80% efficiency, 3,000 L tank र 400 L/day नमुना हुन्। आफ्नो छाना, gutter, local rainfall, tank र प्रयोगअनुसार inputs बदल्नुहोस्।The 80% efficiency, 3,000 L tank, and 400 L/day demand are editable examples. Replace them with your roof, gutters, local rainfall, tank, and use.