How much will it cost to catch rain? When community come together to harvest rain, the per-capita investment goes down. For instance, Panchsheel Park Colony about 1000 residents pooled in Rs 4.5 lakh to harvest more than 170 million litres of water annually. Rainwater harvesting methods are site specific and hence it is difficult to give a generalised cost. But first of all, the major components of a rainwater harvesting system - rain and catchment area - are available free of cost. A good proportion of the expenses would be for the pipe connections. By judiciously fixing up the slopes of roofs and location of rainwater outlets, this could be brought down considerably. However the cost varies widely depending on the availability of existing structures like wells and tanks which can be modified and used for water harvesting. Typically, installing a water harvesting system in a building would cost between Rs 2,000 to 30,000 for buildings of about 300 sq. m. The cost estimate mentioned above is for an existing building. For instance, water harvesting system in the CSE building in Tughlakabad Institutional Area, Delhi, was set up with an investment of Rs 30,000 whereas those in the model projects ranged between Rs 70, 000 and Rs 8 lakh. The costs would be comparatively less if the system were incorporated during the construction of the building itself. Some basic rates of construction activities and materials have been given here, which may be helpful in calculating the total cost of a structure. The list is not comprehensive and contains only important activities meant to provide a rough estimate of the cost. a. Unit cost of construction activities. Item Unit Rate (Rs.) Excavation in soils cu. m. 90.00 Excavation in rock cu. m. 150.00 Brickwork with cement mortar (1:6) cu. m. 1400.00 Plain cement concrete (1:3:6) cu. m. 1500.00 Reinforced cement concrete (1:2:4) cu. m. 4700.00Including steel bars, shuttering etc. cu. m. 4700.00 PVC piping for rainwater pipes  - 110 mm diameter  - 200 mm diameter Metre metre 165.00 275.00 Making borehole in metre 165.00Soft soil (with 150 mm diameter PVC casing) metre 180.00 b. Ferrocement tanks with skeletal cage Capacity of rooftop water harvesting system in litres 5,000 6,000 7,000 9,000 10,000 Total cost in rupees 12,430 12,975 13,970 14,380 15,800 Source: Action for food Production and United Nations Children's Fund, Rooftop rainwater harvesting systems c. Plastic tanks: Available as finished products in various capacities. The cost of these tanks ranges from Rs 2/litre to about Rs 3.5/litre. Other brands available in the market Brand name Unit cost (Rs. Per litre) Hindustan, Jindal 1.80 Storex, Ganga 2.75		Technology Urban People Harvesting System  n Components  n Design  n Construction  n Maintenance Cost AT A GLANCE The Potential Initiative  n Practices  n Projects  n Legislation  n In your building Traditional Practices SEE ALSO No water Water war Look up! How to harvest  n In rural areas    In urban areas Jal yodhas Way ahead READ MORE :

RAIN WATER HARVESTING

	Design of storage tanks The volume of the storage tank can be determined by the following factors: Number of persons in the household: The greater the number of persons, the greater the storage capacity required to achieve the same efficiency of fewer people under the same roof area. Per capita water requirement: This varies from household to household based on habits and also from season to season. Consumption rate has an impact on the storage systems design as well as the duration to which stored rainwater can last. Average annual rainfall Period of water scarcity: Apart from the total rainfall, the pattern of rainfall -whether evenly distributed through the year or concentrated in certain periods will determine the storage requirement. The more distributed the pattern, the lesser the size. Type and size of the catchment:Type of roofing material determines the selection of the runoff coefficient for designs. Size could be assessed by measuring the area covered by the catchment i.e., the length and horizontal width. Larger the catchment, larger the size of the required cistern (tank). Dry season demand versus supply approach In this approach there are three options for determining the volume of storage: Matching the capacity of the tank to the area of the roof Matching the capacity of the tank to the quantity of water required by its users Choosing a tank size that is appropriate in terms of costs, resources and construction methods. In practice the costs, resources and the construction methods tend to limit the tanks to smaller capacities than would otherwise be justified by roof areas or likely needs of consumers. For this reason elaborate calculations aimed at matching tank capacity to roof area is usually unnecessary. However a simplified calculation based on the following factors can give a rough idea of the potential for rainwater colection. Illustration Suppose the system has to be designed for meeting drinking water requirement of a five-member family living in a building with a rooftop area of 100 sq. m. The average annual rainfall in the region is 600 mm (average annual rainfall in Delhi is 611 mm). Daily drinking water requirement per person (drinking and cooking) is 10 litres. Design procedure: Following details are available: Area of the catchment (A) = 100 sq. m. Average annual rainfall (R) = 611 mm (0.61 m) Runoff coefficient (C) = 0.85 1. Calculate the maximum amount of rainfall that can be harvested from the rooftop: Annual water harvesting potential = 100 x 0.6 x 0.85                                                  = 51 cu. m. (51,000 litres) 2. Determine the tank capacity: This is based on the dry period, i.e., the period between the two consecutive rainy seasons. For example, with a monsoon extending over four months, the dry season is of 245 days. 3. Calculate drinking water requirement for the family for the dry season         = 245 x 5 x 10         = 12,250 litres As a safety factor, the tank should be built 20 per cent larger than required, i.e., 14,700 litres. This tank can meet the basic drinking water requirement of a 5-member family for the dry period. A typical size of a rectangular tank constructed in the basement will be about 4.0 m x 4.0 m x 1.0 m Salient features of this approach: Simplest approach to system design but is relevant only in areas where distinct dry seasons exist Provides a rough estimate of storage volume requirements This method does not take into account variations between different years, such as the occurrence of drought years. It also entirely ignores rainfall input and the capacity of the catchment to deliver the runoff necessary to fill the storage tank. This technique can be used in the absence of any rainfall data and is easily understandable to the layperson.These points are especially relevant when designing systems in the remote areas of developing countries where obtaining reliable rainfall data can be difficult.		Technology Urban People Harvesting System  n Components Design   Storage   Recharge  n Construction  n Maintenance  n Cost AT A GLANCE The Potential Initiative  n Practices  n Projects  n Legislation  n In your building Traditional Practices SEE ALSO No water Water war Look up! How to harvest  n In rural areas    In urban areas Jal yodhas Way ahead READ MORE :