Sunday, January 1, 2012

The Sustainability Review – Water Storage

By Mike Forbes, Co-op Volunteer Writer

Last month we talked about calculations with the goal of obtaining realistic numbers of our water consumption.  In talking with a friend he mentioned that looking at your water bill is a simple way for those who live in a city to determine this.  On your bill you’ll see your consumption, typically in cubic feet which is easily converted to gallons by multiplying that number by 7.48.  I thought this would be good to pass on.

Now on to the most challenging aspect of rainwater use, storage. People use various methods such as plastic, wood, and concrete tanks, old dairy trucks, wooden wine barrels, and above ground swimming pools.

Our house water supply which includes drinking water consists of four, dark green 1600 gallon HDPE plastic tanks.  This is probably one of the most foolproof, proven and affordable methods of storing water.  Dark colors are important because algae will grow rapidly in a light colored tank if exposed to light.  Having more than one tank is nice on several fronts. They are easier to handle, readily available, comparably inexpensive (our tanks cost approximately $600 each delivered) and provide redundancy in the event a leak.  The HDPE plastic is the same material that milk jugs are made from and current testing shows that it doesn’t leach chemicals into the water.

Above or below ground?  Above is generally easier but not always practical as water freezes.  Our tanks are located above ground in a room with 2” of foam insulation around them.  I don’t fret about the tanks themselves freezing as it would take a really big cold spell to freeze that much water.  However, I do worry about the plumbing and watch it closely when the temperatures dip below freezing.  In 6 years we have never seen pipe temps below 37 deg F. 

If you decide to go with a below ground tank make sure it is rated for below ground use as they are structurally very different.  On the converse, below ground tanks typically rely on the surrounding dirt for stability and can collapse in on themselves if used above ground (ask me how I know this?).

For most people it’s not going to be realistic to store all the water that falls on their roof as this would take a very large tank(s).  This is where calculating usage is essential to balance what you use with having an adequate supply, even through the dry months of summer.  I analyzed the rainfall data by month and estimated when we would run low.  We go into the summer with full tanks from the spring rains and when July comes we don’t see much rain until September.  The lowest our tanks have been was 750 gallons total at which point we started hoping for rain.  An additional tank would give us a more comfortable buffer.

Many people are going to use rainwater for irrigation only.  In this case many problems are eliminated since you can have storage located outside that is seasonal and drained during the winter months.  I’ve seen many people use wine barrels at the base of their downspouts for this and others place large tanks out in the yard.  As long as you are diligent in draining your system in the fall this can be a very effective setup.  My current plan for larger scale irrigation system is to fill a 24’ above ground swimming pool providing over 13,500 gallons of water.

Water tanks can be sourced locally through Hahn Supply and occasionally craigslist.  A word of caution on used tanks. Many have been used for chemical and fuel storage.  These liquids may have absorbed into the tank and would not be a good choice for drinking water.  I see very few used tanks out there that are suitable for drinking water, not to say one might turn up tomorrow. 

If you are looking for more information, our library has the definitive resource on water storage is Water Storage by Art Ludwig.

Mike can be reached at and welcomes questions/comments.

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