Message from the CEO- Lanka Rain Water Harvesting ForumAs the cost of domestic rainwater harvesting (DRWH) system depends mainly on the size of the tank, it is important to design the tank to ensure optimum performance at tolerable cost. This mathematical stimulation model developed in collaboration with National Building Research Organization (NBRO) supported by USAID is using historical climate data and physical characteristics of the rain harvesting systems such as roof area, roof surface type, first flush volume, effective storage volume and in-house water demand. to calculate the appropriate capacity of the rain water collection tank. This model will significantly benefit householders, designers and planner in Sri Lanka to design rainwater harvesting system to achieve a reliable and cost effective potable/alternative water source.
|Demand Based Calculator||Yield Based Calculator||Feasibility of Proposed Tank||Cost Estimate for RRWHS|
The calculator can calculate the required quantity of water for drinking, cooking, bathing, sanitation, and gardening during long dry spells to fulfill diverse requirements per family. Past survey data of water usage per family in Sri Lanka were embedded therefore end-user can handle it easily, to calculate reliable and precious water requirements, and also, it can handle user-defined values of requirements.
Mathamatical equation used for calculations Tank capacity (m3)=(Number of persons per familty × Water usage per person per day (L) × Number of dry days)/1000
This calculator can calculate the monthly harvestable water volume stand on past rainfall values, user-defined roof catchment type, and area. Moreover, a separate option is provided to insert customized rainfall values without selecting district rainfalls
Mathamatical equation used for calculations Tank capacity (m3) = (Roof Runoff Coefficient × Roof area (m2) × Monthly Rainfall (mm))/1000
Research and Theoritical Values
This calculator can produce a graphical interpretation of the remaining water at the end of the month throughout the year based on proposed tank capacity and water consumption. Also, satisfaction percentage at the end of the particular month upon monthly demand is displayed for better understanding of end-user. This simulation was derived from some assumptions to keep the model simple. (Assumption: remaining water volume at the end of the month will be the water volume to next month consumption and harvestable yield in the same month is added to remaining water volume at the end of the same month)
Mathamatical equation used for calculations
This calculator enables to user to get idea about the construction cost of Rainwater Harvesting System.
Remaining Water Volume at the End of Month (L)
Demand Satisfaction Percentage (%)