How To – Introduction to Rainwater Collection in Residential Construction

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    The collection of rainwater for drinking and general use is not something new but as we have seen in the past 10 years droughts are now common in the USA. As of October 2007 over 40% of the United States is under drought conditions both due to increased building and low amounts of rainfall.

    For these reasons it is important to understand our impact on the land and when we can make modifications that will both save us money and precious water resources. In other HowTos we will cover how we can reduce our use of water but here we will explain the concepts of rainwater collection.

    In general rainwater for use in drinking is a serious commitment. If you live in a location that allows you to collect your water for potable reasons such as drinking and washing of food and your body you need to have not only a clean but pure water reserve. This means that the water that is collected from the roof of your home must be collected and stored in an approved Potable Water container called a Cistern.

    A Cistern is a Tank that is made out of various types of materials. I have seen people make concrete block structures that are lined with a food grade rubber material and there are off the shelf Plastic Stainless Steel and Aluminum Cisterns that are manufactured and past testing for drinking water. There are also lower grade Cisterns that are made of plastics that can only be used for gray water uses like washing clothes and flushing toilets. And the lowest grade containers are only good for watering landscaping and may not be suitable for vegetable gardens.

    This is a very important aspect to rainwater collection that can not be overlooked because if the tank that you store the water in has been previously used for petroleum or pesticides there is no way to ever clean it well enough for human consumption. Additionally as said above there are different grades of Plastic containers and although you may save a few hundred dollars the lower grade containers are never good enough for drinking water. Always ask for Potable Water containers and if you decide to build your own tank ask for a Potable or Food Grade Liner that looks just like a Swimming Pool Liner but can be used to make safe container tanks.

    Ok so now we know that we will collect the water from our roof and we will store it in a potable grade container if we are drinking it.

    Well how do we get it off the roof into the container and where do we put the container?

    When you purchase your container you can buy either above ground or below ground containers that can withstand someone walking over them. If you have the option below ground is great because it frees up area in your yard.  If you are thinking about using rainwater for your total needs you may need to install up to a 10,000 gallon water tank which is rather large. Something of that size is about 10’x10’x10′ or a 10 foot cube of water. 

    If you are installing a smaller tank you can locate it above ground but either choice you make you should allow for easy access to the manhole because you will need to check and add chemicals to your water every few months. A total clean out and scrub down should be performed between 12 and 18 months depending on your location.

    To get the water from the roof into the tank you will use your rain gutters but you will need to make some adjustments to them. If you have a 3″ gutter you may want to increase the size. Your down spouts will need to be retrofitted with a roof washer clean out which will allow the first hundred gallons of water to be discarded because it will contain dirt from the roof.  The rest of the water can be piped to your tank with PVC pipe. Although it is recommended that you use CPVC pipe in external applications  because it is UV protected the plain schedule 20 or 40 PVC waste pipe that you get at your supply store will last a long time. You could even paint the outside with latex paint to extend its life but it is probably not necessary.

    Now that the water is in your tank you need a way to get it back out so you can use it.  A shallow Well pump is your best bet they cost about $100 and can supply your whole house or give you enough pressure to water your garden and lawn.  Most are rated at about a 50 foot head which means they can push the water up to the second story of the home.

    Before you can drink your water it must be filtered and decontaminated. Some home owners use a chemical treatment in the tank which is why you should allow easy access to your tank at all times even if it is buried. Other home owners use a Mechanical filter that everyone has seen at the home stores but to purify the water you will also need a UV Light Filter that basically exposes the water to UV Light and frys the bacteria. Proper instillation of UV Filters is important and you must maintain them so you will either need extensive research or a professional to install one correctly.

    Well thats about it you collect the water off your roof and store it in a tank then use a Well pump to feed it into the house and filter it before the connection to your regular house water supply.

    What we have not covered here is the proper design of the system, the selection and use of Filters and Chemicals to purify your water and the different methods of using Rainwater and altering your homes plumbing so rainwater can be used for drinking or just for washing and flushing toilets.

    There is a lot more to it but this is the basics and prior to about 1800 most homes around the world used either a Cistern or a Well to drink and wash from. The important difference today is we have the ability to clean the water to a level that is safe.

    The total cost of a Cistern Rainwater System can run from about $1500 to $5000 if you have someone install it for you. This means the turn around payback is somewhere between 2 and 5 years depending on your location and rainfall levels.

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