Part two of the rainwater harvesting series brings us to water storage tank materials. The first question I had was what are the most common materials and does it make a difference which material I choose? What I found is that the two most common tanks materials to choose from are corrugated steel or polyethylene (plastic). There are other options out there (cement, stainless steel, and other varieties of metal), but they’re not as common. Based on my findings, here is my conclusion: go with plastic unless you plan to collect truly massive amounts of water, in which case a metal storage container might be a better fit.
Plastic tanks have these things going for them:
- Light weight (low shipping cost)
- Easy to move and install
- Come in a wider variety of sizes and shapes
- Won’t rust over time
There – that was easy enough. Now on to the next hurdle.
Next you have to figure out what size tank to get. Now obviously this is going to depend on whether you plan to use your tank for potable water, non-potable water or irrigation only. This water consumption calculator will allow you to pick and choose what water use you want to account for and since I plan to use the collected rainwater for non-potable water only, I left out shower and bath, faucet and dishwashing water. The rest (irrigation, toilet and laundry) added up to 24,820 gallons per year or 98 gallons per day. And on a side note, by owning a high efficiency washing machine we’re able to save roughly 5,000 gallons of water per year!
Now given that my hypothetical home in Texas would only be able to collect 19,737 gallons of rainwater per year (according to the calculations in part 1 of this series), I wouldn’t be able to harvest enough rain to cover my daily non-potable water use. Basically, I’d need a bigger roof. So let’s say for the sake of argument that my roof was a bit larger and it could collect enough water to cover my daily water use of 98 gallons.
With that number in hand we can work the rest of the equation, though for “most days without rain” I’ll be using a hypothetical 21 days:
Most Days without Rain X Average Daily Water Use = Storage Volume Required on Day One of a Dry Spell
21 days x 98 gal./day = 2,058 gallons
So in order to last three weeks with no rain using only harvested water for all non-potable purposes, I would need to have 2,058 gallons on hand before the dry spell hit. Based on these results, personally, I would purchase a 2,500 gallon poly/plastic tank that would cost anywhere between $800-$1300. This size tank can be purchased online at places like plastic-mart.com or watertanks.com. Keep in mind these calculations only serve as guidelines. Reality is that the dry spell could come at a time when your tank is only half full so take these equations with a grain of salt.
Check out how simple it looks to install this 9,000 gallon dry system:
And that concludes part two of this series. I think I’ll spread this out to include a third part that covers the other important components of a rainwater collection system and any other points to consider before deciding whether to have one installed or install one on your own. I’ll drop some more knowledge tomorrow, so stay tuned.
- Pt. 3: Rain Harvesting for Your Home: All the Parts - Constant Craftsman - DIY Projects for Arts and Crafts Style Homes