Is Rainwater Harvesting Feasible?

The correct terminology is actually Rainwater Catchment Systems, i.e. rainbarrels and storage tanks.

A new home without any landscape (a clean slate to work with) allows for all of the sustainably progressive principles to be implemented without the need to retrofit and is usually the more feasible option. The only limitations are the site characteristics and the budget of the homeowner depending on the level of systems designed into the landscape.

Anyone with a roof without rain gutters and downspouts will soon find out their problem areas and where the water tends to accumulate on the ground due to inadequate surface grading and drainage. That water may or may not fall in a desirable location. It may have to be drained away either on surface drainage or underground lines. In order to capture that rainfall for reuse, however, downspouts and gutters are a must.

Having no gutters or downspouts however allows the homeowner or landscape designer to design a rainwater catch system and integrate the location of the downspouts with the storage devices whether they are rain barrels or larger cisterns or storage tanks.

The irrigation system for the planting areas can be designed around the use of rainwater. If an automatic irrigation system is used, the pressure being delivered to the valves must be of sufficient pressure to allow the valves to function. Conversely, a low flow drip system set up based on gravity flow can work for certain areas of the yard where the elevation distances are adequate.

Most homeowners who start out rainwater harvesting using a barrel or several soon realize they are actually losing out on capturing a large amount of water. A typical 55 gallon barrel can fill up in only one hour with a 1/8” of rain on 1000 square feet of roof area. Not only does it fill up quickly thus losing out on the rest of the potential water, but you will soon use up the water in the barrel far in advance of the periods of no rain when having saved water for use during the dry periods is really the whole point in storing water. Water catchment systems should not be looked at so much as water harvesting systems, but as water catchment storage systems. It’s like when a squirrel saves nuts for the winter hibernation.

With a larger storage capacity a more sophisticated system is required, one with booster pumps that can be used to pump water for use in the automatic irrigation system as well as for hoses to wash cars, or other garden hose activity requiring a certain amount of pressure to function.

The low tech benefits of capturing rainwater include a passive gravity fed drip system for a specific garden area, containers or other plant irrigation needs that is downhill from the barrel. You can also tap the spigot and fill up a watering can and water houseplants with the rain water. But you must ask yourself, if I am using this water now, will I have any during the periods between rains?

This is the point where serious rainwater catchment systems replace the novel rain barrel. One quickly realizes that the point is to not just capture the water, but to store it for the dry periods between rain.

The question of feasibility is both a factor of your site suitability and economics. Here are some site suitability factors:

·       Adequate roof catchment (sufficient area and fitted with gutters and downspouts)

·       Suitability of area at base of downspouts to accomodate the plumbing necessary to channel the water into barrels or a storage device

·       Number of suitable downspouts relative to required storage desires.

·       Aesthetics of plumbing, tanks and trenching needs

The cost of implementing a system that is designed to pump water out to a garden, an accessory garden hose or other high pressure use can signficantly add to the cost of an otherwise passive gravity flow system. Most serious rainwater storage systems pump the water to where it is designed to be used, otherwise, you must rely on gravity flow alone and the use must therefore be down hill from the output elevation of the storage tanks.

You may compare the cost of a rainwater catchment system vs. the cost savings of paying for the water and realize that water is so cheap that you will never break even. In this case, the economics is not important, rather, its the lifestyle and ecological stewardship values that drive your decisions.

The flip side of the cost savings is not letting all of that water go to waste, capturing it and using it wisely while at the same time, curtailing your need for municipal water supplies.

JSL Landscape Certified Rainwater Professional 

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John Stuart Leslie John Stuart Leslie, MLA, Licensed Landscape Contractor holds a Masters in Landscape Architecture where he studied Xeriscape, Permaculture and Natural Ecosystem Design and Planning.