Rainwater Harvesting and Conservation in Home Designs

Water--it's a necessity for life but we take it for granted and waste so much. Rainwater harvesting is not a ‘new thing’ or some ‘green fad’–civilizations have been collecting and storing water for millennia in various forms and for different uses.

Rainwater is free to collect in Texas, but it does take some effort and expense--hence, those of you on city water supply pay to have instant water at your taps and faucets. There is the collection, storage, treatment, and delivery, all so you can drink it, bathe in it, water the garden, wash the car, and flush the toilet.

A modern rainwater harvesting system designed for residential use.

My wife and I have a whole-house rainwater collection system. We can store approximately 15,000 gallons of water and that is our only supply of water. It took some convincing to persuade her to go off-the-grid for our water, especially when we live in a subdivision with town water, but we have been living this way now for almost 10 years and it’s working pretty well. There are maintenance and expenses involved, but we are certainly saving more than we would be spending if we were connected to the local municipal supply--and as a bonus, our water isn’t treated with who-knows-what chemicals.

I am not going to encourage you to build a whole-house rainwater harvesting collection system like ours due to the maintenance – not everybody wants to be committed at that level. If you are interested, I can certainly work with you--designing your dream home that is also more gentle on the environment. However, I am going to encourage you to incorporate a rainwater harvesting collection system into your designs and to use rainwater to flush toilets.

Rainwater Harvest Collection Rates

The Greater Austin Area has an average rainfall of approximately 36 inches of rain per year. For every one inch of rainfall on a 1000 sqf roof, you have the potential to collect approximately 620 gallons of water. This collection potential certainly adds-up quickly over a year – approximately 22,320 gallons per year. That’s around the same amount of water that is in a swimming pool 30 ft long x 20 ft wide and 5 ft deep--a big pool, and that is only from a 1000 sqf roof.

As you can see, you do not need a large house to start to make a difference when it comes to water conservation.

Simple Water Conservation Methods

There are all manners of water saving devices that can be installed while building a new home or retroactively installed in an existing home; examples include low-flow taps, energy and water efficient appliances, and dual-flush toilets that use a fraction of water that older cisterns use.

You do not need treated, potable water to flush the toilet. With some simple filtration and maintenance, a family of four can certainly reduce their environmental footprint by using rainwater for this purpose. A considerable amount of residential daily water use is flushed down the toilet and here is where the savings can be made.

Rainwater Collection and Usage for Flushing Toilets

An efficient toilet will use around 1.1 gallons of water per flush. If a family of four use the toilet five times each per day, they will use 22 gallons of water each day just flushing the toilet. This equals 8,030 gallons of water per year. As previously mentioned, a 1000 sqf roof will provide approximately 22,320 gallons of water per year, providing more than enough water for a households toilet use. We all know that Texas is subject to drought and flood, but if you have two 1500 gallon rainwater tanks, this will provide enough water for flushing per the above calculations for 136 days.

To fill these tanks, you would need approximately five inches of rain (based on a 1000 sqf roof) to fill them, providing you with enough water to flush the toilet for over four months. I know that at times, it can be a while between measurable rainfall in Texas but we typically do get rain at least every four months. If you increase the collection area and the storage capacity, you can increase that collection significantly.

Rainwater Harvesting Expenses and Tax Exemptions

As previously mentioned, there are expenses involved in the design and installation of a system such as this, but there also numerous tax benefits. There are currently no restrictions on rainwater harvesting in the State of Texas and it is actually encouraged by state laws. You can apply for a sales-tax exemption certificate for the purchase of any materials or components used for the capture and storage of rainwater (see https://comptroller.texas.gov/forms/01-339.pdf - the items purchased are classified as rainwater harvesting equipment or supplies, which are exempt from sales tax under Texas Tax Code Section 151.355).

You can also apply for a Property Tax Exemption for any structures housing rainwater tanks with your local Appraisal District. The forms for this exemption are also available from the Texas Comptrollers Office (see https://comptroller.texas.gov/forms/50-270.pdf)

Environmental Benefits of Rainwater Harvesting

There are also environmental benefits with rainwater harvesting, including reduced run-off, erosion, and flooding, and reducing your use of potable water. Our population is growing but our dams and aquifers are not getting any larger. The more people that draw from these sources will also reduce their levels even faster.

By reducing your dependance on municipal water supplies, you can help slow the reduction in these levels. And don’t forget that, when you flush your toilet, the water is being sent back into the environment--whether it be into the town sewer system for treatment or your own septic field, the water is still being put back into the ground for nature to recycle it.

If you still are not interested in the associated work and expenses of rainwater harvesting for flushing your toilets, why not consider it just for irrigation purposes? Your plants, veggies and lawn will appreciate an additional 22,000 gallons of rainwater per year with a simplified system.

Conclusion

In closing, harvesting rainwater so it can be used to flush toilets (or for irrigation purposes) will help reduce our dependance on municipal water supplies.

Natural rainwater is better for plants than treated town water. Rather than wasting this precious commodity and allowing it to wash down the road, creek, or drain, retaining it for future use will help our dwindling supplies and help the environment in various ways.

Implementing some basic elements into a new or existing home will pay dividends in the future while helping to preserve this valuable resource.