7 Things to Know About Harvesting Potable Rainwater

I have been obsessed with developing sustainable water supplies for years, but it took me that long to begin looking into rainwater harvesting. As I observed a declining static water level (the number one factor I use in sizing a pump for wells), I began to consider rainwater as  a back-up to my other developed water sources. See my post on the uses of rainwater. I quickly realized the greater potential that rainwater has and it led me to installing a potable rainwater catchment system in my own home. The result: rooftop water landing in my drinking cup through a 7 layer filtration system. In this article, I’ll be reviewing those 7 layers of filtration that will deliver safe, clean drinking water directly from your roof. The first 4 layers are necessary for any high quality, non-potable catchment system, and the last 3 make it potable. 

Layer 1: Gutter Gaurds

To remove large debris coming from your roof, you will need some type of leaf screen along the gutter or in the down Sprout. I like to use the Leaf Relief because it can handle high speed flows off of my 12/12 pitch metal roof, and it makes a strong box out of my gutter system. It is important to clean out your leaf screens regularly to prevent clogging and the build-up of bacteria or leaf decay.

Layer 2: First Flush Diverter

Our roofs often contain a mini ecosystem of smaller contaminates  such as dust, pollen, insect bodies, animal feces, or pesticides. You will need a first flush diverter to give your system a chance to rid itself of this debris. The FFD (first flush diverter) is located between the gutter guard and the tank and routes the first flow of water from the roof away from the storage tank. This first flow can be routed to a garden or planted area. I have written in more detail about how FFD’s work, how to size them, and the type I prefer in my guide to rainwater harvesting.

Layer 3: Overflow Skimmer

Once the rainwater enters the tank, you will find an overflow skimmer to be of great benefit to your catchment system. Overflow siphons will keep your tank from overflowing and at the same time remove the lightest surface contaminates from your tank. This photo shows the particles collected in my overflow skimmer. This layer will also give you a cleaner upper water zone and nicer intake for the next layer.

Layer 4: Floating Extractor

Research has shown that the cleanest zone of rainwater in your storage tank is about 4 inches below the top of the water. The floating extractor is designed to extract water from this level. This is much better than drawing water from the bottom of the tank where heavy sediment settles, and also avoids the small skimming particles from the top. 

This completes the filtration layers needed for non-potable water. Don’t forget to check out my post on the uses of rainwater. The next 3 layers are added so that you can bring your rainwater safely into your kitchen.

The harvested rainwater will enter these last 3 filters through a pump system. Information about rainwater pump systems can be found in my guide to rainwater harvesting.

Layer 5: Spindown Filter

The Rusco Spindown Filer uses the momentum of the water to “fling” particles out of the stream, which settle in the bottom of the filter. The spin down gets easily rinsed through the bottom valve, can be back-flushed, and used over and over again. It doesn’t need a replacement filter, but serves to greatly increase the life of the canister filters that follow. 

Layer 6: Filter Canister

After the Rusco, I use Whole House Filter Canister from 5, 10, and 20 microns. It is a good goal to filter to 5 microns with these canisters. They will help your ceramic filter (next layer) stay clean, but need to be changed regularly, depending on filter size and input quality. 

Layer 7: Ceramic Filter

The ceramic filter puts a great clean finish on your potable water setup. It should be filtered to 5 microns before entering to help it stay clean longer (less cleaning means less chances of breaking the ceramic candles). 

Make sure you always test your harvest before using it as potable water. I go into full detail about each system component, as well as bonus features such as improved drainage and hot rainwater showers in my guide to rainwater harvesting. It can be downloaded as an ebook below and can be easily read on a mobile device.  

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