Water Collection Part 2: Storing Water
After you have determined the size, location, and material of your water tank or cistern, ensuring that the tank has these essential components is your highest priority. If built and maintained properly, a water tank or cistern with these parts will be able to provide clean water efficiently and reliably for a long time with a minimized risk of complication or failure. The Important Pieces The Inlet is the pipe that delivers the water from the source(s) to the tank. This must be attached to the tank above the highest possible water level, which is determined by the overflow (explained next). This prevents the water in the tank from flowing back into the inlet and backing things up wherever the water is coming from. If possible, you should install a diversion or shutoff valve close to where the inlet arrives at and empties into the tank so that you can stop the flow when the time comes for cleaning and maintenance or just in case there is an emergency with the tank that must be addressed. The Overflow is another pipe near the top of the tank that drains excess water when the tank gets full, preventing the water from splashing over the edge of the tank or flowing back into the Inlet. The height of the Overflow drain determines the water level, so placement is critical. Depending on the size of the tank, every vertical inch can equate hundreds of gallons of water storage, so you don’t want to aim too low. The Overflow also serves and extremely useful second function. When left in a large tank for a long time, most of the particles and debris that come in with the water will either float to the surface or sink to the bottom, leaving the water in the large middle part (where you pull your water from) nearly perfectly clean. If the mouth of the overflow is oriented horizontally so that it opens towards the tank’s ceiling and a funnel like extension is added to widen the circumference of the opening, then most of the water draining out will be this dirty surface layer, minimizing the loss of clean, usable water. The Outlet is the pipe that will take water from the tank to deliver it to its end use such as irrigation and washing clothes or, if being used for drinking, cleaning, and other uses with high purity requirements, it will travel from the outlet through a proper filtration system before being delivered to its end use. To ensure you have access to as much of your clean stored water as possible, the outlet is usually located near the bottom of the tank. Due to the purifying settling effect mentioned earlier, there will be a layer of sediment that pools at the very bottom of the tank, with much cleaner water above. The Outlet should be installed as low as possible without allowing this sediment to be sucked out with the clean water. This can be as low as 6” above the floor on large (50,000 Gallon) tanks and perhaps lower on smaller cisterns. The Drain is an important component when the time comes to empty the tank for cleaning or maintenance. The Drain is a pipe leading out of the tank, usually with a control valve or cap on the outlet, and can be located on the wall or the floor of your tank depending on what works best for your situation. However, to avoid leaving a reservoir of sediment, it should be installed at the tank floor’s lowest point to ensure the entire volume can be emptied without needing to bucket and sponge dirty water out of the tank by hand. If possible, designing a sump (a spot where the floor dips down below the level of the rest of the floor) into your tank with a drain located at the bottom of the sump can help ensure effective drainage. If the drain line is short and your tank drains directly to the ground around itself, a concrete “tongue” should be installed at the drain’s outlet to direct the water out and away, preventing the water from eroding the earth out from underneath your tank, which could put it at risk of tipping or collapsing. The Access is the way people can enter and exit the tank when checking water levels or performing cleaning and maintenance. This is usually an opening with a lid installed on the tank’s roof above the water level, so that the tank can be accessed when it is full. There are two very important safety measures that must be taken with the Access. The first is to make sure that the access has a lid that can be locked shut to keep out critters and curious children for whom the tank can be a drowning hazard. As an alternative or additional measure for limiting unauthorized access, the ladder to the Access can be designed to be removed and stored elsewhere when not in use. The second important measure is making sure there is a way to get in AND out of the tank. A few ladder rungs or a climbing rope mounted to the interior walls of the tank can make falling in inconvenient rather than dangerous. The Air Vent is the final of the essential components and is responsible for allowing air to escape and enter the tank as the water level rises and falls. It is usually located atop the tank and does not need to be very large, because the rate of air movement will generally be slow. It is important to ensure that the Vent (along with all other components) is built in such a way that prevents sunlight, insects, and small animals from entering the tank. This is important because sunlight and water together will inevitably become a home for life such as algae, which will attract more uninvited guests who will build a food chain in your potential drinking water. Making sure your tank is shaded from direct sun as much as possible will keep water temperature down, preventing algae growth and bringing cooler water to the tap. Critter proofing the tank with screens or valves at every point of access is also important because the tank is for water and water only, rats and squirrels need not apply. While these are the most important components for a tank that can effectively and efficiently store clean water with minimal maintenance, there are many more ways you can improve the tank’s functionality and convenience. Much of the information in this blog post and more can be found in greater detail in Art Ludwig’s book “Water Storage”, one of a series of books that cover the many ways to harvest, store, use, and reuse the water falling or flowing on, in, or near your own home. If you are thinking of adding cisterns to your home’s existing water system or are building a new home and would like to include local water harvesting and storage features in the design, books like these can help you move forward with confidence in your own understanding of what you need to do and how it can best be accomplished, as well as advice from any neighbors or friends who have built similar systems for their own homes. Finally, if you are in doubt or your design requires expertise beyond what you can do alone, engineers and professional designers can help you make sure the system is safe, secure, and legal. Good luck! Written by James Drumwright IV, Architectural Designer at H2D Architecture + Design
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