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Rainwater Harvesting

Do you know that Rainwater can be used to meet your daily water demand?

Kathmandu Valley receives approximately 1300-1600 millimeters of rain every year. This means that on a typical rooftop of 100 square meters more than 160,000 liters of rain is available for capture and use.

Why use Rainwater?

  • Alternate source of water during monsoon
  • Offset groundwater
  • Save money on buying tanker water
  • Help in reducing urban flooding

Process of Rainwater Harvesting

Rainwater harvesting is the process of collecting rainwater from falling on the rooftops of the building, filtering and storing it for future use. In doing so, rainwater gets managed at the source to meet the water demand.

  1. Rainwater from the roof is channeled to the RapidSand Filter, via pipes.
  2. The RapidSand Filter consists of layers of filter media and comes with an inbuilt First Flush system which flushes out the first rain containing the maximum debris.
  3. The filter media then removes the remaining dirt and debris from the rainwater.
  4. The filtered water is then diverted to the underground reserve tank via pipes and stored for future usage.
  5. This filtered water can be used for cooking and other daily utility purpose.

SmartPaani RapidSand Filters (RSF):

SmartPaani’s RapidSand Filter is a customized rainwater harvesting system. This system consists of first flush device which flushes out the first rain containing the maximum debris. This is followed by a customized rapid sand filter consisting of layers of filter media which remove the remaining dirt and debris and reduce bacteria from the rainwater. The RapidSand filter is sized according to the roof size of the building.

SmartPaani systems come in the following sizes depending on the roof size:

  • SmartPaani 200 RSF
  • SmartPaani 300 RSF
  • SmartPaani 500 RSF


Rainwater Harvesting is the collection and utilization of the rain that falls on rooftops and other surfaces for immediate and future use. This is done either by using storage tanks or recharging the rainwater into underground sources such as wells. SmartPaani Team creates customized solutions based on specific needs and space availability.
Solutions range from tank-based storage for all uses during the rainy season, groundwater recharge for year-round water supply, or tank storage for year-round drinking and cooking uses.

No. Rainwater is pure. Rooftops are dirty, but filters can easily remove contaminants. We have installed systems where people use ONLY rainwater for drinking year round. Simple filtration or chlorination can make rainwater fit for drinking.

No. In fact it can be very economical. It is a one time investment and we estimate that more than 20% of the population in Kathmandu would benefit more from harvesting their own rainwater than putting in other high return investments. Some clients have been able to recover the invested amount in a year.

Three reasons:
1. This is not always the case and becoming increasingly less so. The current demand for water is 320 Million Liters Per Day while the supply is only 120 Million Liters a Day in the Monsoon. In 2002 the demand was 140 Million Liters a Day; every day the water situation becomes worse for somebody even in the monsoon, tomorrow that person could be you. More than 15% of Kathmandu’s population purchases tankers of water year round, meaning they spend more than 30,000 rupees a year on water.

2. Convenience; More than half of the people have to get up between 12 and 6 a.m. to deal with water, even during the monsoon. If you use the storage tank in your house to collect rainwater this inconvenience is avoided. Additionally the occasional urban flooding that affect municipal supply, especially during the monsoon, will no longer be a problem during this time.

3. Groundwater – Most people we talked to used to have abundant water in their tube wells 15 years ago, but do not today. Why? Over pumping – No. The main problem is that the rain that used to go into the groundwater is now sent to the sewer. More rainwater inside the Ring Road is sent to the sewer than the much-hyped Melamchi will provide in a year. 15 years ago this figure was half. Before this water used to percolate into the ground and much of it remained for dry season consumption, this is no longer the case. SmartPaani can work with you to begin to help recharging this “wasted” rainwater into your well.
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