Rainwater Harvesting – Everything You Need to Know

Rainwater harvesting on a household scale is a great way to obtain free water for your home or garden. The three main challenges with collecting rainwater are storage capacity, maintaining good water pressure when using the collected rainwater to water your plants, and, if you plan to use rainwater in your home, filtering and purifying the rainwater.

On a global scale, rainwater collection not only helps communities in drought-affected areas to harvest crops that might otherwise not ripen without water, but it can actually help improve the lives and education of children in those areas.

Not only does the collected rainwater get used for everything from drinking and cooking and laundry, to watering garden plots for local food production, but in many communities where these rainwater harvesting cisterns are installed, children who used to spend much of their day carrying water buckets to and back from a water source, can instead focus on attending school and improving their education.

The collection system for many of these rainwater harvesting cisterns is the roof of the local school.

And because the regions where these cisterns are installed have a rainy season and a dry season, there’s no shortage of rain in the rainy season to fill the tanks; the rainwater harvesting then provides water to the communities for much of the dry season.

Encouraging citizens to participate

In many locations, the city government started an ambitious program to encourage homeowners to install rain barrels that would gather rainwater from their downspouts.

Why would a local government pay its residents to collect rainwater?

By encouraging people to capture at least one barrel full of rainwater at each downpour – and by requiring anyone installing a rain barrel, or for that matter anyone building a new house or doing a major renovation, to disconnect their downspouts and send the stormwater onto their lawn or garden, the city was able to significantly reduce the incidences of sanitary sewer water overflowing into the lake. Our beaches are now much cleaner than they were when I was a kid, and I swim in Lake Ontario at least a few times every summer.

Of course, installing a rain barrel is only the first step; you also have to¬†use the harvested rainwater. Most of the rain barrels typically have an outlet at the bottom to which you connect a garden hose, but with at most 3-4 feet of headroom you get barely any water pressure on the garden hose even if the tank is full (which it won’t be, on a sunny day, as soon as you start watering).

To make a rain barrel truly effective you either need it higher up than the area being watered (for instance, if your home is on a sloped lot) or you need to add water pressure by using an inline water pump such as the one shown at right, or a garden pond pump if it supports both in-line and submersible modes. (Note that garden pumps are rated in gallons per hour; a typical garden hose will flow at 3-5 gallons per minute (GPM), so a 150 GPH garden pump won’t even hit the lower end of that range. Of course, a typical 55 gallon rain barrel will empty in about 22 minutes even with a slow 150 GPH garden pump.

Drinking rainwater

You might be tempted to drink the rainwater you harvest off your roof. And while it’s perfectly fine to open your mouth to the sky on a rainy day and drink what falls in, you should be careful about drinking rainwater collected from your roof. That’s because the rainwater picks up contaminants from the roof and gutters and downspouts – potentially including tar and granules from shingles, aluminum or ferrous oxides from aluminum or steel gutters and downspouts, and decomposing plant matter from within the gutters. There is a risk of both chemical and biological contamination, although the risk is not that significant. My uncle has been drinking rainwater for twenty years, collected from the roof of his home. He keeps his gutters clean; he collects the rainwater in a large bucket, then strains it through loose activated charcoal poured into a paper coffee filter, which sits in its coffee funnel above a 5-gallon springwater carboy. The activated charcoal removes the dusty taste and (he hopes) some of the harmful chemicals that might have come off the roof.

Another alternative is to harvest rainwater into a storage container, and then use a camping water filter to hand-pump water out of the storage container into jugs or bottles. We use a camping filter on summer canoe trips to purify water from Ontario lakes (since there is a risk of getting giardia, or ‘beaver fever’, from drinking lake water); the filter drives water through a ceramic filter which removes pathogens.

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