HOW do you capture rainwater?

System design should be aimed at meeting your needs in terms of complexity and cost, while conforming to the given area’s structural design, surface areas and their permeability, water storage capacity, and landscaping.

Often, homeowners start their water harvesting systems with a simple berm or contour to divert runoff otherwise lost from their property into a tree basin. Over time, more contours, mulching, and storage systems can be gradually added.

Some basic techniques are:

Contouring: Surface runoff can be directed to turfed areas or shallow basins around trees and shrubs by contouring the land surface. These contours need not be more than an inch or two in height, and can have a barely perceptible slope, so large amounts of earth-moving is not required. The goal is to collect the runoff, direct it to where it can be of use, and slow it down so it has time to soak into the ground. This can reduce erosion on your property. Contouring can be done by creating microbasins, contoured swales, drains, and gabions.

Water storage in cisterns: Rain that falls onto roofs can not only be directed to landscape plants, it can be stored in tanks or rain barrels for later use. Such a system can be as simple as a downspout feeding rain into a 55-gallon barrel. More complex systems can include filters and pumps. Below-ground cisterns can store both rooftop and surface runoff. Whether investing in a rainwater storage system makes sense or not will depend on the frequency and volume of rain as well as its seasonal distribution, the size of your roof, your irrigation needs, and other factors.

If it hasn’t rained in quite some time, the initial runoff from a roof or driveway can be loaded with pollutants, including motor oil and bird droppings. Water storage systems can be designed so that the initial runoff is not stored. Information on flushing systems is available at http://ag.arizona.edu/cochise/waterwise/first_flush_diverters.pdf.

Mulching: Swales and basins can be mulched to reduce rainwater evaporation from soils and retain soil moisture for the plants and trees.

A model for calculating your storage needs that considers your catchment surface area, roof type, and landscaping is coming soon. Check back for updates. Other calculation methods can be found within the Literature and Print Resources section of this website.