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Tue, Feb. 18

Column: Is rainwater harvesting a good investment?
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Plastic tanks such as this one are the most common containers used for rainwater harvesting. (Courier file)

Plastic tanks such as this one are the most common containers used for rainwater harvesting. (Courier file)


There have been a number of discussions recently concerning uncontrolled building development in the Prescott area, and the impact on our limited water supply. Rainwater harvesting has been put forward as one of many potential solutions.

However, is harvesting residential rainwater a good investment financially? In certain areas of the country, catching rainwater for household use and irrigation can be a cost-effective solution, but not all. It is said that rainwater harvesting is most suitable in those areas that receive plenty of rainfall. However, for only irrigation, this makes no sense!

Rainwater harvesting collects, filters, stores and distributes rainwater for irrigation and for various other purposes. Rainwater is free from many chemicals found in groundwater, making it ideal for irrigation. In fact, storing large reservoirs of harvested water is a great idea for areas where forest fires and bush fires are common year-round. It also lessens the burden of soil erosion in a number of areas, allowing the land to thrive.

As such, there is little need for building vast infrastructure for the rainwater harvesting system as most rooftops act as a workable catchment area, which can be linked to the storage and distribution system. With the increase in population, the demand for water is continuously increasing. This has led to a significant depletion of ground water in arid areas such as Prescott, where there is a developing water scarcity.

Unfortunately, many homeowners associations do not allow above-ground barrels or tanks as they take up valuable space and can be an eyesore if not landscaped correctly. It will take a state or city ordinance to override these rules, and maybe when the water runs out they will.

Rainwater is an economical, safe and sustainable source of quality water when it is captured and stored in the correct manner. The storage tank is one of the most important components of the system, typically being the most expensive and the most permanent. When choosing the size of a storage tank, consider several variables: rainwater supply (local precipitation), use demand, projected length of dry spells without rain, catchment surface area, aesthetics, personal preference and, of course, your budget.

Some tanks are suited for above-ground placement, where others can be used both above- and below-ground. A water storage container can be made of metal, fiberglass, polyethylene (plastic), poured concrete, concrete blocks, stone or wood.

Polyethylene tanks are the most common. They vary greatly in size, shape and color, and can be used above- or below-ground. For buried installation, specially designed and reinforced tanks are necessary to withstand soil expansion and contraction. Polyethylene tanks are comparatively inexpensive, lightweight, and long-lasting and are available in capacities from small 50-gallon barrels to large 10,000-gallon tanks.

Some of the challenges of rainwater harvesting are that rainfall events are highly unpredictable, and cannot be relied upon as a long-term stable source of water without municipal or well backup. The capital cost for a rainwater harvesting system is typically higher than the cost of obtaining water from a centralized distribution system. They also require care and maintenance after installation as they may get prone to rodents, mosquitoes, algae growth and insects.

General guidelines for tanks include:

• Before you start, conserve as much water as you can. Cutting your water usage will reduce the size of tank you need and save you money.

• Make sure the tank is easy to access and maintain.

• Tank should be opaque or darker, either upon purchase or painted later, to inhibit algae growth.

• Tanks must be covered and vents screened to discourage mosquito breeding.

• Install first-flush and screening devices prior to water reaching the tanks to keep it as clean as possible.

• Buried tanks should be located in well-drained soil and location.

• Water weighs about 8 pounds per gallon so plan your pad, if any, before installing your tank.

• Plan where storage tank overflow should be piped. Keep it away from underneath your holding tank to prevent pad erosion and to keep animals away.

Next time we will establish the amount of annual rainfall in the area (Prescott, Arizona), how much water can be collected from the catchment area, how to size the ideal rainwater system and perform a financial return on investment analysis.

Find Paul Scrivens at

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