Solutions for harvesting rainwater depend primarily on the needs of the end-user and the size of the house, however little it may be. Nevertheless, collection systems are similar, even though those for larger buildings, including multi-residential applications, are much more complicated in terms of plumbing.

Personal motivation to harvest rainwater is varied and includes a desire to reduce water bills substantially, to minimize the overloading of stormwater systems and possible flooding, and to lessen the stress placed on existing infrastructure, including dams.

Whatever the reason, if you want to harvest rainwater for a small home, where do you start?

Firstly, you need to understand some of the basic principles about harvesting rainwater, and then you need to know how it is done. You might also want to enlist the assistance of a mechanical, electrical, and plumbing (MEP) engineer who has experience in the field.

Rainwater Harvesting Basics

The most common rainwater harvesting systems divert water from the roofs of homes and other buildings, usually via gutters and downspouts, and then channel it into some tank or cistern for later use.

Most commonly, harvested rainwater is used to provide an inexpensive source of water for irrigation, as well as for sanitation, including flushing toilets and washing clothes and dishes, as well as fire protection, and to augment any other existing supplies of water.

Some people depend entirely on rainwater for all their needs, including water for drinking. While rainwater required for non-potable needs is commonly filtered and disinfected, if it is going to be used as (potable) drinking water, it will need additional treatment to ensure it is safe and healthy to consume.

In 2018, an international standard for rainwater harvesting systems was published by the International Code Council (ICC) and CSA Group that develops standards, giving people the direction needed to harvest rainwater acceptably. Developed for use in both Canada and the U.S., the standard addresses a myriad of issues that relate to water technology, plumbing, and public health. More specifically, the standard addresses the needs for both potable and non-potable applications and provides the tools necessary to ensure that the quality of water is right for its potable or non-potable end-use.

The standard specifically covers residential applications, including single-family residences, which is the category any little house would fall into. And most importantly, it provides specifications for a water safety plan just like all other rainwater systems. This plan must be developed by, or at very least approved by, an MEP engineering firm in Chicago, New York, Los Angeles, or whichever city, town, or rural area you live in.

Sloping metal roofs are favored for rainwater harvesting systems because they get rid of contaminants quicker, and allow the water to run off more quickly, which also gets rid of pollutants quicker.

* Tips for Harvesting Rainwater:

The components required for any rainwater harvesting system include rain barrels, tanks, or cisterns that need to be screened from light to prevent algae growth. Both materials (metal and plastic are common) and colors vary, but darker hues are preferred because they minimize the penetration of light. There are different grades of the tank, and they need to be fit for purpose. For instance, those used to store potable water must be rated as such and should incorporate an air gap or reduced pressure backflow system that prevents cross-contamination of water supplied by the local municipality. FDA-approved polyethylene resin is a good option for potable water tanks.

The size tank you choose will be in keeping with the quantity of water you and your family are likely to be able to use. Remember there’s no point in storing large quantities of water that you cannot use in your little house or irrigate your yard and veggie garden.

* The cost will also be a factor:

The other choice will be whether to site the tank below or above ground. The latter is considerably cheaper, and installation is a lot quicker and more comfortable.
Gutters should be at least five inches wide, and in areas where it snows in winter, there should be gutter hangers at 12-inch intervals to carry the extra potential weight. Gutters should also be installed with a slope of at least 1/16-inch for improved drainage and to avoid any possible ice build-up during the winter months.

Both wind- and water-borne debris can be a problem. It is advisable to used gutter outlets that are rounded to help reduce the build-up of debris. Additionally, installing the gutter so that it’s a half-inch lower in front helps to minimize splashing of debris against the wall. Installation of a leaf screen over tops of downspouts is a must, and first flush diverters should installed to prevent debris and other contaminants from entering the tank. A good rule of thumb is to install one 10-gallon diverter for every 1,000 square feet of the roof or other catchment areas. Inline sediment filters can also be installed to get rid of sediment that forms between the tanks and outlet. These are invaluable for drip-line irrigation systems, to prevent any sediment from clogging the drip-line holes.
Note that because sediment settles to the bottom of tanks, the last four inches of water in tanks shouldn’t be drained.

Other important elements of rainwater harvesting systems include:

  • An overflow that will release excess water when it rains heavily.
  • A vent to prevent a vacuum effect inside the tank. This opening must be covered with mesh to prevent contaminants and insects from entering the tank.
  • An inspection port near the top of the tank. This can also be used for maintenance issues.

If rainwater is treated to make it potable, this must be done according to relevant specifications. Various methods may be used, including ultra-filtration, chlorination, UV-light radiation, or ozonation.

Whether you use the services of an engineer to design a rainwater harvesting system for your little house or simplify the system so you can do-it-yourself, you can be sure that it will be a cost-effective investment that can make a significant difference to your life and the environment.

Written by:

Michael Tobias is the founder and principal of  New York Engineers, an Inc 5000 Fastest Growing Company in America. He leads a team of more than 30 mechanical, electrical, plumbing, and fire protection engineers from the company headquarters in New York City, and has led numerous projects in New York, New Jersey, Chicago, Pennsylvania, Connecticut, Florida, Maryland, and California, as well as Singapore and Malaysia. He specializes in sustainable building technology.

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