Rainwater Storage

During my permaculture certification program and supplementary reading, I learned of many benefits of irrigation with rainwater. (1) Rainwater picks up nitrogen as it falls through the atmosphere, which is 78% nitrogen. The nitrogen is then available to plants as a necessary nutrient. (2) Tap water is treated with chlorine and other chemicals, which can be harmful to vegetables, especially seedlings. (3) People regularly report improved growth and production of vegetables irrigated with rainwater instead of tap water. On top of these considerations, my municipality charges an annual “drainage fee” based on impervious surface that contributes to the storm sewer system. Installing some type of rainwater diversion and storage seemed like a logical solution to help me avoid drainage fees and provide the best water for vegetables.

The question is: what type of rainwater storage to install?  Some of the options I considered are:

Option 1: a 500-1,000 gallon metal rain tank (http://metalraintanks.com),

Option 2: a rain barrel setup purchased from my municipal truckload sale (http://www.rainbarrelprogram.org/Houston)

Option 3: a series of 55 gallon plastic drums configured in series to the quantity of storage desired,

Option 4: a 500-1,000 gallon plastic tank (http://www.tank-depot.com/productdetails.aspx?part=EP-ESL-790WO).

Some of my specific considerations were:

(1) Value for the price. I was aiming to spend about $1-1.50/gallon of storage.

(2) Durability. The system should be mostly maintenance free and last 10 years.

(3) Shape. The location available for this tank is on my side yard, which is about 10′ wide and bordered by my house and a wooden fence. I needed a system that would not obstruct passage through this space and also not be an eyesore.

(4) Size. I used rain gauge data from a nearby rain gauge (waterdata.usgs.gov) to calculate rainfall frequencies and graphed cumulative demand and frequency distribution. Based on my goals of irrigating specific areas (the vegetable garden) and running out of rain no more than once per year (during the driest period), I determined the minimum size I would need is 500 gallons. Less detailed tools are available at some agriculture extension offices (e.g., http://rainwaterharvesting.tamu.edu/catchment-area/).

Based on these factors, I identified the following limitations to each option:

Option 1: the metal rain tank system bumps the upper end of my value criteria and a minimum 1,000 gallon size would be needed to bring the cost per gallon <$2.00.  It is the most durable option. On the other hand, a future homeowner may not want rainwater storage. Perhaps the most limiting issue: the shapes available do not meet my needs. A 6’ diameter would obstruct too much space on my side yard. In addition, the shipping cost could be extensive and the ability to transport the thing into my side yard through a small gate and around the house is questionable. Option 1 is a no-go.

Option 2: The truckload sale only offers 50 gallon plastic tanks for $69. Although the price per gallon is reasonable, this does not meet my storage needs. If I was to purchase 10 of these and line them up on the side yard, I expect that would be an eyesore.  Option 2 is a no-go.

Option 3: This seemed like a good option if I could find these plastic containers at a good price. On some online classified pages I’ve seen them sold used (food-grade) for $25 each. This certainly meets the value criteria, but would require a number of other purchases (e.g., diverter system, PVC connections between tanks, frame for storing them if they will be stacked). Although these could be stacked for more consolidated storage than Option 2, the need for about 10 of them still detracts from the aesthetic appearance of my side yard. In addition, I’m not a plumbing expert and the plumbing necessary to configure this option was intimidating. Option 3 remains in the running.

Option 4: The slimline water storage tanks were cheaper than the metal tanks and fit my space restrictions much better. Although not as durable, this has a 5-year warranty and probably would have lasted as long as I expect to live in my house. However, as with Option 3, the installation issue was intimidating. In hindsight, I wish I picked this option.

After weighing these options over a period of 6 months or more, and calculating the additional cost savings I would achieve from a reduced water bill on an annual basis (~$50/year), I came across a fifth option. Secondrain.com sells kits to construct rain benches. For about $300 I could purchase the liners, diverter, and the plumbing components to get me started for 560 gallons worth of rainwater storage. This was by far the cheapest, most aesthetically pleasing option. And with the plumbing components to get me started, I didn’t need to be intimidated about how to hook it up! I would just need to purchase wood to construct the benches.

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