Strategies and Techniques for Successful Rainwater Harvesting
Collection of rainwater is one of the easiest, most effective ways to to implement sustainable living practices. Around the world, rainwater historically has been collected for a multitude of uses, including irrigation, drinking water for household use or livestock, air conditioning, aquaculture, groundwater recharge and control of fires. The act of gathering, accumulating and storing rainwater is commonly referred to as rainwater harvesting or catchment.
Advantages of Rainwater Harvesting
- Conservation of the the local water supply.
- Water is low in salts and chemicals and is an excellent source for irrigation, gardens, houseplants, pets and livestock.
- The controlled collection of rainwater reduces erosion and flooding.
- Helps to recharge groundwater tables, springs, wells, and rivers.
Although the quality of captured rainwater is likely to fall somewhere between that of groundwater and surface water, it can be an effective alternative source of water for many household uses.
Disadvantages of Rainwater Harvesting
- As rainwater may be contaminated, it is often not considered suitable for drinking without treatment.
- Rainwater harvested from roofs can contain animal and bird feces, dirt and pollutants, pesticides, or mosses and lichens.
- The collection method is crucial in determining what type of treatment may be required, if the harvested rainwater is to be used for human consumption.
In order to successfully plan and set up a rainwater harvesting system, there are a number of rules or principles that should be followed. These steps, as well as a brief description of each, are as follows:
- Do a thorough mapping of the property and calculate potential "rain cache". This would entail evaluating your property as a whole as far as
observing how rainfall currently disperses naturally; where it may pool, what plants and areas of your yard require water, how to optimize shade versus sun
exposure to reduce energy bills, etc. To calculate the potential amount of rainwater your useable space might generate annually, simply take the average expected
rainfall per year and multiply it by your "catchment" area (the square footage of your yard, roof, whatever available space you plan to utilize for collection).
To convert this to gallons per year of harvested rainwater, multiply by the conversion factor 7.48 gallons/cubic feet. Here is the equation:
CATCHMENT AREA (ft2) x RAINFALL (ft) x 7.48 gal/ft3 = TOTAL AVAILABLE RAINWATER (gal/year)
- Select an appropriate rainwater cistern. Based on the calculations and observations made in the previous step, selection of your rainwater storage tank (or cistern)
should be made. Capacity should be based on expected runoff versus the water needs of the residents of the home and landscape. A cistern can be either made from existing materials
or the options for pre-manufactured cisterns include light-proof, dark-green or black polyurethane plastic, corrugated metal, and fiberglass.
- Plan your collection of rainwater from the highest point first, then work your way down. Most likely your roof will be the highest point, so
you will want to assess where your raingutters are currently directing the water, and revise accordingly. Your cistern should be located at a position where
optimally it is no further from your garden (if applicable) than 25 feet, to reduce water pressure loss. Considerations such as shading, privacy, and distance to the areas
that require the usage of the water should all be factored in when choosing your cistern location.
- Consider and plan for potential overflow situations. In the case of a rogue storm which exceeds the capacity of your setup, be prepared to manage the overflow.
An overflow pipe can be used which directs the excess to trees or natural drainage areas such as the street.
- Harvest the rain close to where it falls naturally. Simple water-harvesting earthworks throughout your yard such as basins, terraces, contour berms, and check dams will harvest the rain effectively, directly where it falls.
One easy method to create water-harvesting earthworks is to dig level-bottomed basins and infuse with about 4 inches of mulch, starting at the higher areas of the property and working downward.
The mulch will enrich the soil and combined with the roots of plants create a sponge-effect, while improving the soil’s ability to infiltrate.
- Allow water to spread and infiltrate the landscape slowly. Sometimes easier said than done, a strategy should be in place to spread the water throughout the landscape
in a controlled fashion. The cistern(s) and mulched earthworks should provide this function, along with raised pathways and gathering areas throughout the property.
Creating a pattern of “high and dry” regions that drain to adjoining basins kept “sunken and moist” will help to define those areas through vegetation while spreading and sinking the flow of water.
- Ensure you have sufficient living groundcover. To avoid pooling water (and the creation of pesky mosquitoes) the optimum scenario is achieve a balance between the rate of water infiltration in to the ground
versus losses due to evaporation. Always try to stick with native plants in your landscaping choices -- if you live in an area with minimal rainfall, desert plants which require less water will be the sensible choice.
- Continually reassess your system and improve it. Similar to life in general, there will always be changes and tweaks that you will need to make over time to stay "on top of the game".