Outdoor demand is based upon a small low-water use landscape with minimal handheld irrigation; persons intending to irrigate larger areas or a vegetable garden, will need a larger catchment area and larger storage capacity to accommodate both indoor demand and outdoor irrigation in larger quantities.

Please note that in the Average Rainfall scenario, the water in storage may eventually exceed the capacity of the cistern, which puts an effective limit on the end-of-month storage amount. 

This calculator is provided for general guidance only. Design and installation of RWH facilities should be based on site-specific conditions and technical expertise.

Irrigation Demand Estimates

 
 
 
 
 
 

Please note that in the median rainfall scenario illustrated, the water in storage may eventually exceed the capacity of the cistern, which puts an effective limit on the end-of-month storage amount. 

* Irrigation Factor is cacluated by multiplying average historical potential evapotranspiration by 0.6 (a turf coefficient for warm season turfgrasses) and subtracting rainfall from the result. Data can be found at http://texaset.tamu.edu. As an alternative one can use historic data specific to one's own community. A limited dataset is availalble at the TAMU site.

This table is for general guidance only. Site-specific irrigation demands may also be calculated by other methods, or as recommended by local water management professionals.

  
AP AgriLife Ext RWH Calculator

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Hazen Williams Pressure Loss Calculator

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