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Is A Rainwater System Right For You?

As we all adjust to the changing climate, you may find yourself wondering if a rainwater system is right for you. Increasing drought in summer months has led to more intense water restrictions for home, land and business owners. Over the years Hill Country Rainwater has assisted hundreds of home and business owners explore the various contributing factors in order to make an informed decision.

Coming up in this post:

  • What purpose will the rainwater system serve?

  • How much rainwater can you collect?

  • How much water are you likely to use?

  • What size of rainwater tank fits?

What purpose will the rainwater system serve?

One of the first questions we ask is what is your plan for the water? Determining this can help us ascertain likely system requirements. For example, a collection system solely for irrigation purposes does not have the same components as a filtered system for potable, in-home use.

This consideration may also be impacted by current water source availability. If your home or business is currently on a city water source, there will likely be some specific regulations and requirements to meet when installing your system. Over the last several years of drought in central Texas, we at Hill Country Rainwater have increasingly received calls from concerned home and ranch owners looking for solutions to keep their gardens and livestock well watered during the long, hot summer months. If you find yourself in this situation, a rainwater system might be the right solution for you!

Currently on a well? No problem! We have installed many systems which will allow you to select between well or rainwater depending on the water's usage and allow you to send rain water to some places and well water to others. (Typically home owners opt to use the rainwater in the home and the well water for gardening, irrigation or other outdoor uses.

How much rainwater can you collect?

Total rainwater collection amount depends on two factors: the surface area you plan to collect from, and the average annual rainfall for your area. On average, one square foot of collection surface collects .62 gallons for each inch of rain. For example, depending on where you hang your hat in the Texas Hill Country, you might get an average of 36 inches of rain each year.

Multiply the average rainfall by the square footage of your collection surface to determine approximately how much rainwater you d collect. Let's say you have 2000 square feet from which to collect, and you live in an area with an average of 36" of rainfall per year. You're looking at an estimated total annual collection of around 44,640 gallons! Take a peek at the chart below for some examples of different central Texas counties and their potential total annual rainwater collection based on the collection surface area. For those customers building new homes consider who would like to inexpensively increase collection surface AND provide higher quality of life we suggest enlarging your overhangs and, especially, your covered porches - proper overhangs create comfortable more energy efficient homes and larger porches are always appreciated during the many months of indoor/outdoor living we enjoy here in central Texas.

County (Avg Rainfall)

1000 sq ft collection area

2000 sq ft collection area

5000 sq ft collection area

Hays (36")

22,320 gallons

44,640 gallons

111,600 gallons

Blanco (34")

21,080 gallons

42,160 gallons

105,400 gallons

Comal (33")

20,460 gallons

40,920 gallons

102,300 gallons

Are you fretting about needing an enormous tank to contain all that rainwater? Fear not; that rain is spread out over the year, not (thankfully) in a single annual deluge. Also, there is the factor of consumption, which we address in the next section.

Alternatively, perhaps you're concerned that you won't have enough water. We have some potential solutions to offer for that as well.

How much water are you likely to use?

This question may be challenging if you are not actively monitoring your water usage. According to the Texas Water Development Board, the average residential water usage per person is 86 gallons per day, but our experience has taught us that, though everyone is different, rainwater households use less water than the average, closer to about 50 gallons per person per day. Multiplying this number by the number of people using the water is a good guide for determining your average monthly water usage.

Using the chart above and estimating that a family of 4 lives in a 5000 square foot home in Hays county, we can see that their annual collection could total 111600 gallons and their annual usage is about 73000 gallons, which results in a water surplus of about 40000 gallons for this example family!

Considering all these factors, now we can take a look at what tank size will be best suited to your needs and your space.

What size of rainwater tank fits?

Depending on where you reside, available space may dictate how large of a rainwater tank can be installed. Important factors to consider at this point include the tools installation process. Most larger rainwater collection systems require the use of heavy machinery such as a skid-steer or mini-excavator. Does your space allow for this type of equipment?

Regarding the tank itself, let's continue with our example family of four in Hays County. Taking into consideration the estimated annual collection, and the average monthly usage, we would typically recommend a 31,000 gallon tank which has a 27' diameter and is about 7'6" tall. Now you can take your tape measure outside and determine how much tank you could actually fit in your space. To calculate the basic tank size we'd recommend for you, take your predicted total annual amount multiply it by .9 to account for system losses and divide that number by 3 to account for 4 months without rain (unlikely but possible). For our illustrative family of 4 living in a 5000 sf home, we'd take the 111,600 gallons x .9 to get 100,440 and divide by three to reach and ideal tank size of : 33480. Because this rain cistern size falls between two tank sizes we'd offer the client the option of a 31K gallon tank and a 38K gallon tank with diameters of 27 and 30' respectively.


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