Pt. 1: Rain Harvesting for Your Home – The Basics

Pt. 1: Rain Harvesting for Your Home – The Basics

Apr 27, 2009 |  by  |  Water Conservation  |  Share

After reading the rainwater harvesting blog entry on, I got to thinking about the topic again in a much larger capacity than my two previous articles on the subject. I started thinking that a rainbarrel sounds pretty wussy-like. I mean, if you’re going to collect rain, collect some RAIN – use it for non-potable purposes such as toilet flushing, washing clothes, and garden/lawn irrigation. And seeing as how we intend on moving to Texas in about a year, harvesting rain will be of even greater importance to us since the amount of rainfall throughout the year in those parts can be pretty slim.

So the first order of business is to do some calculations. I used the rainwater collection calculator at The Tank Depot to do the math for me. And found the annual rainfall of my area at Weatherbase. What I found is the following:

Living in Austin, Texas (annual rainfall of 32 inches) in a house with a footprint of 1100 sq. ft., that’s able to collect water from 90% of the footprint (the high percent is based on installing a “wet system” where the collection pipes are located underground allowing multiple downspouts from different gutters to be connected) there is the capability to collect 19736.6 gallons of rainwater from our roof per year. That amount will decrease a bit after accounting for first flush loss and evaporation loss from the roof surface. First flush is the initial water that comes off the roof and is collected in a water diverter. This water can contain some pretty nasty stuff like bird poo, bacteria from dead bugs, and concentrated tannic acid. The diagram below shows how the diverter works in keeping your water supply contamination free.
.first flush diagram1 Pt. 1: Rain Harvesting for Your Home – The Basics

The next step is to decide if you want a wet or dry system. A dry system is one where the water runs directly from the gutters into the tank. This means the tank needs to be fairly close to your home, which may not be ideal in every situation. The term “dry” is based on the fact that there is never any standing water in the pipes. So no stagnant water and no chance of mosquitos having babies all up in your system. The wet system, as I mentioned earlier, is one where the pipes from one or more gutters go underground and up into the tank. This type of setup is necessary when the tank is placed far away from the home. Because the pipes are underground, even when there is no rain there is still water in the pipes. Every opening in the underground pipes needs to have proper screens to keep out mosquitoes. And according to Rainwater Harvesting, an Australian company specializing in rainwater products, you can convert a wet system to a dry system by installing in-ground water diverters. I won’t go into detail on that process but I recommend you check out their article on what it takes to make the conversion.

Then you need to decide if you want your tank above or below ground. Above ground tanks are cheaper and faster to install but probably won’t add much aesthetically to your landscape unless you live out in the country and have a lot of space to place the tank far enough away from your home to not become an eyesore. Underground tanks on the other hand are hidden and take up very little space. Since we intend on owning some acreage at our new Texas home, an above ground tank will work fine for us. Excavation costs aren’t cheap and we’d rather apply those savings to other projects.

So that’s it for the first part of this series. Check back tomorrow when I’ll cover tank materials, tank sizes, and some of the important components that make up an efficient rainwater collection system.

pixel Pt. 1: Rain Harvesting for Your Home – The Basics

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