Rainwater Catchment: Is Rainwater Harvesting Worth It?

Rainwater harvesting can be a great way to lower your water bill, as the natural precipitation can be used for different purposes. The upfront costs of a rainwater catchment system vary, depending on the amount of water you want to store and its intended uses. The simplest type of catchment system involves purchasing a rain barrel and connecting it to the existing gutter system with tubing or additional downspouts. The rain is stored in the barrel and used to irrigate gardens, plants, and lawns.

More complex systems can store water for household use. This can be a great way to lower the water bill, but the equipment must include filters and other features to treat the water and make it potable (meaning safe for the people to use and even drink). Purifying options range from chemicals like chlorine to ultra-violet lights. Despite the need for filters, rainwater has one major advantage besides its low cost: it does not need a water softener because the water is naturally pure.

It should be noted that complex systems that create, store, and deliver water to the household require regular cleaning and maintenance. Therefore, even though the water itself is technically free, there are regular costs associated with owning a rainwater catchment system.

Is Rainwater Harvesting Equipment a Good Investment?

Like the initial costs, the return on investment of a catchment system depends on the intended usage of the harvested rainwater. In areas with high water costs or in homes that rely on well water, a simple rain barrel setup that is meant to harvest and store water for garden and lawn irrigation can pay for itself quickly. Many arid or drought-prone regions have restrictions on lawn watering, and a rain barrel system can be an excellent way to get around these rules.

If water use is expensive, capturing precipitation to use in the household can also be worthwhile. The cost of such a system depends on its size and the technology used. Homeowners can get a rough estimate by figuring out how large of a system they require; the average cost will work out to roughly $3 to $6 per gallon of storage space. Systems at the higher end of this range will be below ground (as opposed to above ground) and will require multiple pumps and filters to create potable water and bring it into the home. Considering this, a 4,000-gallon system might cost $15,000. The amount of time it takes to recoup the investment will depend on the cost of water from the local utility provider.

For a house that averages a monthly water bill of $125, the new system will pay for itself in 10 years (if it provides for all the home’s water needs). Of course, it will take longer if the house is still connected to the local water supply and the harvesting setup provides only a percentage of the overall water needs.

Important Questions to Answer

Homeowners who want to consider rainwater catchment need to look at their current buildings and see if the project will involve simply installing the tanks, purifier, and pumps, or if other changes are needed as well. The University of Hawaii’s College of Tropical Agriculture and Human Resources has published advice about considerations for the existing infrastructure of buildings that are considering rainwater catchment.

The publication advises owners to examine all roofing materials. This is important, as all types of catchment setups rely on the roof and gutters to collect water. However, certain materials can contaminate this water and make it unsuitable for irrigation or human use. For example, galvanized roofing may contain high amounts of zinc. Copper flashing may have traces of lead or unhealthy amounts of copper. These materials may need to be replaced at least neutralized by adding a non-toxic coating to the top of the roof.

The university also suggests trimming back trees so that animals cannot access the roof and potentially contaminate the water. Regularly cleaning the roof and removing debris from the gutters will also help keep the harvested water clean enough that the filters and purification equipment can make it potable. Most of the systems that harvest for home use have a screen that provides a “first flush” to keep large particles and debris from entering the piping and potentially clogging filters.

How Big Does the System Need to be?

The American Rainwater Catchment Systems Association (ARCSA) has published a system sizing chart. The math that they use for the equations is somewhat complex because it takes into account different variables, including:

• The efficiency of the collection setup
• The size of the roof
• The average rainfall for the particular climate

The ARCSA does provide a downloadable Excel spreadsheet you can use to plug in numbers for your specific situation. With the spreadsheet, you can see exactly what size tank is needed, and whether the system will likely cover your home’s water needs for the year.

Catchment Systems for Gardening

During a rain shower with one inch of precipitation, an average roof on a 30-by-50-foot house will catch 900 gallons of water. That is a considerable amount. How can you take advantage of all this rainfall? The average rain barrel holds about 50 gallons of water, so it would take 18 barrels to fully harness that free water. Installing an 18-barrel system just for gardening is not practical, however.

A more realistic option is to divert the water directly to the soil. That might seem counter-intuitive at first: the rain is already falling on the garden during a storm, so why would you need to water it more? The answer lies in something that agriculture experts call “field capacity.” This idea focuses on the amount of water that the soil is capable of retaining. Soil is made up of small particles, and each particle retains a given amount of moisture. Gardeners can run hoses from the top of their rain barrels through their garden and use the excess water (everything that will not fit in the rain barrel) to saturate the soil. This could lengthen the time before the next necessary watering from your rain barrel reserves.

How to Pay for a New Rainwater Catchment System

Rainwater catchment systems of all types can seem pricey. Even those who only plan to harvest rainwater for their garden or landscaping may discover they need a pump, a gutter upgrade, and new piping. Since rainwater catchment systems can increase a home’s efficiency in the long term, they tend to qualify for property assessed clean energy financing (PACE financing). PACE programs can help homeowners deal with the payback period in a practical way.

With PACE, a property owner can finance eligible water conservation projects for no upfront cost, and then pay for the improvement overtime—as a line item on their property tax bill. Any savings on their water bill can be put towards the cost of their water catchment system. For projects that qualify, PACE can help offset the potentially steep upfront costs of a catchment upgrade.

Discover how PACE financing can help you save water and live more sustainably – call Ygrene at (855) 901-3999 or email: info@ygreneworks.com.