Collecting and Storing Rainwater: The Planning Stage
While publicly provided water is often the default choice of home builders and owners because of its convenience of access and use, more and more people are choosing to harvest and store their own water on site to use for irrigation, cleaning, washing, flushing, and drinking. This can be done to supplement or completely replace public water. Some hope to save money or gain complete financial freedom from the utility companies, while others hope to reduce their demand on the environment, as public water requires considerable energy to move from source to user, and it is rarely extracted without impacting the ecosystems that we share the water with. For people living beyond the reach of municipal services as well as those in the cities, having a reserve of water at your home provides security against seasonal shortages, droughts, and even emergencies such as fire (some insurance companies appreciate these measures! See what your insurer says about it).
Those of you who have on site access to a source of water may be considering finding some way to hold on to it for your own use rather than watching it all flow by, whether it is a spring, a stream, a well, or rain falling on your roof. While the easiest and cheapest use for on-site water storage is meeting irrigation needs, it is possible for those of you building a new home or renovating your current home to integrate your tank or cistern both visually and functionally with the house itself for indoor uses if you are willing to include the code-required filtration measures. Before going shopping, you will need to determine how big your tank will need to be, where it will need to be placed or built, and what material it should be made from, followed by making sure your tank has all the basic components necessary to provide clean water for a long time with as little trouble as possible. Knowing these things first will help you understand/estimate the associated costs up front and allow you to approach designers, builders, plumbers, or tank and cistern manufacturers with more confidence in the feasibility of your plan.
First and foremost, you will want to figure out how big your tank will need to be, because not running out of water is a top priority. This is determined by balancing the amount of water coming from your source against the amount of water being withdrawn for use throughout the year. Using another real-life example, if you know that you will spend more than you will make in December because of the holidays, then you can set aside the excess income from previous months so that you know it will be there when you need it. For a gardener storing rainwater harvested from their roof, they know that they will need their water in the summer, but most of it will be harvested over the colder months while the rains are frequent. Their tank will need to be big enough to harvest enough through the colder months to provide all summer. Someone who has a spring or well producing a set number of gallons per minute year round may have some needs met on demand no problem, but using the washing machine while someone else showers and a third person cleans dishes will need more water for those 20 minutes than the spring can provide. Their tank will collect the steady stream while nobody uses it (overnight) and then be able to provide for the “peak demand” when it comes (usually in the afternoon/evening), and may not need to be as large as the gardener’s.
If you are also planning for drought or fire protection, this volume may need to be considered separately from what is provided for everyday use. You can use your water bill to begin to understand your home’s water needs, and further research at home and online can further help you pin down the GPD (gallons per day) your house uses. If this number is beyond what your source can provide for, consider the introduction of water saving fixtures, appliances, and habits that can bring demand down if you haven’t already. The rate that your source produces water will also need to be measured as accurately as possible, so as not to misjudge availability. For rainwater harvesting, there are explanations on how to calculate the harvesting potential of your roof and site in our previous blog entry on rainwater harvesting, as well as local climate data on annual and monthly rainfall available online.
After you know how big your tank(s) will be, you will be able to determine where it should go. Limitations on your site such as size, city codes, and location of existing structures may do much to make the decision for you, but where possible you should account for both the location of the water source and the point(s) of use, which would be your home’s plumbing fixtures and/or your garden. Placing the tank below the source and above the point of use allows gravity to provide both pressure and flow for your water as it moves from the source to the sink, so to speak. This saves energy and can decrease or eliminate the need for pumps, saving money and preventing the undesirable possibility that you will lose access to your water if the pumps lose power or break down, although some appliances or uses will need more pressure than gravity can produce, making a small pump necessary. Tanks and cisterns can be installed on solid ground, underground, or atop a structure like a roof or water tower. If you find that placing the tank underground or on a structure are the best options, you will probably need the help of an engineer to ensure the safety and stability of the design. Buried tanks can collapse under soil pressure when they aren’t completely full if they aren’t made specifically for being buried. These tanks will also likely require pumps to access the water, and can be more difficult or inconvenient to access for cleaning and maintenance. Tanks on roofs or other elevated structures require adequate structural stability to handle the massive load of hundreds or thousands of gallons of water, so professional assistance from an engineer will likely be necessary to ensure that your design is safe.
Finally, you will want to know what material your tank will be made of. While the material’s ability to meet your tanks design’s structural requirements is very important, it is also important to consider that the water you store and use will spend a lot of time in contact with the tank itself, and different materials can have different effects on the water’s toxicity and taste. For example, glass is an ideal storage medium for small to medium sized applications because it is completely inert (non-toxic) and does not affect the water’s taste, while plastics (PVC especially) can leach small amounts of harmful toxins into the water over time and make it taste like plastic if the tank is exposed to the sun during the day. In Western Washington, Douglas Fir and Western Red Cedar rain barrels will seem a visually appealing option that naturally resists rot. However, the stuff that makes this wood smell good and resist rot is toxic, and can seep into any water in contact with the wood. While this consideration is important for any people/plants/animals that will use the water, cost and availability will also likely affect your decision. Galvanized steel and concrete can both be very expensive, plastic is often cheaper. If you look around your neighborhood or online, you could find used drums and barrels being sold or even given away. This can be a good quick solution that keeps costs down, but make sure that the container in question did not previously hold any hazardous or toxic materials. If this cannot be determined, be a very cautious buyer, as this container will be holding your water. The other cost of any material is the environmental cost. Production of new steel requires enormous amounts of energy and generates considerable waste material that does not return quickly or cleanly to Earth’s natural systems, and both steel and petroleum-based plastics are non-renewable resources. In this regard, it is important to know what your tank is made of, where it comes from, and to utilize reused or recycled materials where possible.
These are the essential design considerations to tackle when planning out your water storage system, and with this information in hand, you can feel more confident shopping for and applying your design solution to the problem of water security. If for any reason you feel you cannot tackle some or any of the above questions, there are professional designers and engineers who are willing and able to help you realize your water storage dreams. Feel free to see who in your area works with or specializes in home-scale water storage and other “green” living practices. For those who want more in-depth knowledge of water system design, much of the information in this post and more can be found in the water harvesting and storage related books by Art Ludwig and Brad Lancaster, who both have written extensively about their experience designing and building water systems in many different economic situations, scales, and locations. Additionally, we will cover the essential parts and pieces of an effective water storage system for any who would like to read further. Thank you for reading!
Written by: James Drumwright IV, Architectural Designer at H2D Architecture + Design
