Fill up the rainwater tank

In late March, as we neared completion of construction on their new home, the sisters --Candy and Sue -- began to fret just a bit. “There’s been no rain. Should we go ahead and buy some water for the tank?” Wayne shook his head. “Wait,” he told them. “Let’s see what happens. April showers, right?”

We broke ground in October. It took just a little over six months to build their home. The 30,000 gallon rainwater tank was one of the first things to be installed, and we had a truck deliver about 2,000 gallons of water for use during construction. The metal roof went on in December. (If you’re collecting rainwater, you want a metal roof.) Gutters and pipes were installed in January, and they were connected and ready for rain in February. And then it didn’t rain. And it didn’t rain. Remember?


And then came April, woohoo. A couple of good storms the first two weeks of April dumped up to four inches of rain in the area. Now, we didn’t have a rain gauge to the measure the specific rainfall at Candy and Sue’s house. But take a look at the photo and see what happened. I snapped this photo in mid-April. The red bobber indicates the tank’s water level. Almost half full, right? How is that possible, with just 4” or so of rain?

Well, get out a pencil, and let’s do the math.

The sisters’ house has 3,532 square feet of air conditioned space. Add the garage, front porch, the lovely screened porch at the back of the house, and two-foot eaves on all sides, and you’ve got 5,661 square feet of total house coverage. The roof surface is a whopping 6,289 square feet.

Got all that? Now here’s the magic: One inch of rain on 1,000 square feet yields about 600 gallons of water. Every time it rains one inch, the sisters harvest 3,773.4 gallons of water, or about 12% of the tank’s capacity. Those 4 inches of rain during the first two weeks of April produced about 15,093 gallons of water. The tank is half full.

If you’ve lived long enough in central Texas, you’ve figured out by now that our rain often comes in big bucketfuls all at once. Yes, we’ve got water problems in Texas, but the answer falls from the sky. We’re all drinking rainwater; it’s just that some people choose to catch and store it locally instead of waiting for it to flow into rivers, lakes, and aquifers, where it’s stored and later pumped miles and miles (at great cost) to reach homes and businesses.

The sisters decided to invest in a 30,000 gallon tank rather than a 20,000 gallon tank in order to have extra storage capacity to capture as much rainfall as possible during the “rainy” periods of the year. Chris Maxwell-Gaines of Innovative Water Solutions, who designed and installed the system, calculates that a “20,000-gallon tank would be sufficient to supply a 4-person household. Their system should allow them ample water supply even during drought years.”

Of course, the way the home operates and the behavior of its inhabitants have a lot to do with water use. Naturally, the sisters’ home was designed, built, and furnished to conserve water -- the way the plumbing runs were laid out, the water heating system, the water-saving plumbing fixtures. A moderately conservative person might use around 50 gallons of water indoors. Outdoors, the sisters plan to leave the landscape in a natural state, so they won’t be using much water outdoors. However, they have installed a pool/spa that holds 1,500 gallons of water. Once it’s filled, it will need to be replenished occasionally. And the sisters do anticipate occasional long-term house guests. Installing the bigger 30,000-gallon tank has given them peace of mind.

You might be asking about now, “But is it really feasible to supply an entire household with its potable water from a rainwater harvesting system?” Yes. Here's what Chris Maxwell-Gaines of Innovative Water Solutions had to say in a report to the lender's underwriter:

For more evidence of the ability of rainwater harvesting systems to supply an entire household with its water, my company conducted a survey of about 70 of our potable water system owners in 2012. We asked them to look back over 2011 which was one of the worst year of drought since the 1950s. In 2011, our region only received about 16” of rainfall. We found that only 30% of the homeowners had to get water delivered during the year and a majority of this 30% only had to get one water delivery. It is our best guess and experience that due to the conservation technology of the rainwater systems, property owners use a much smaller quantity of water since they can directly see the entire supply of water for their household. Contrast this with a home that is supplied by a well: The homeowners can’t determine how much water is left in their well as they can with a rainwater harvesting system. If the water level in their rainwater cistern is getting low, they can proactively change their water usage patterns in order to extend their water supply. The costs to top-off their systems, which is a rarity, should not average more than a few hundred dollars per year according to cost data received from local water delivery companies in our region.

Question: "You mean, I can buy water for my rain tank?" Sure, you can buy a little water if you need it, say a couple thousand gallons to tide you over 'til the next big rain. You can buy water and store it in a rain tank. You can't buy and store water in a well that's gone dry.

Overall, rainwater as the sole water source for a home is more sustainable, more durable, more secure, and less costly over time than a well. Plus, you know where your water comes from and . . . you know what? It sure does taste good.

Question: "What about financing?" It is possible to get financing for a rainwater harvesting system as the sole source of water for a residence, but it requires a lender who knows how to get it done. The financing for the sisters' project was arranged by Green Energy Money, whose appraisal process quantifies the homeowner's return on investment for energy efficiencies -- and for rainwater harvesting. Security National Mortgage Company provided the permanent financing. Plus, the sisters' home is in Hays County, which offers a property tax exemption for water conservation initiatives, including rainwater harvesting.

Want to know more? Drop us a line, or leave a comment, and I'll ask Chris Maxwell-Gaines to weigh in and help answer any questions.

-- Mary

See our Resources page for links to more information about rainwater harvesting.