In this Rain Tanks Series post, we outline common recommendations on what to do and what not to do when practicing rainwater harvesting. Many of the following do and don’ts of rainwater harvesting are listed with an explanation and further information.
Do
- Know what the collected rainwater will be used for.
- This will help in planning the system design and what needs to be purchased.
- Know how much rainwater will need to be collected.
- This will help in budgeting and preparing the area for use.
- Know the volume of rainwater that can be collected based on where you live and catchment area size.
- This will help in choosing the right rainwater tank and whether the catchment area needs to be changed to increase capture volume. More details on how much rainwater can be collected and how to calculate it can be found here.
- Know what size rainwater collection tank is needed.
- This will ensure enough rainwater is collected and stored for use, including during dry seasons. For more information, see this post on what size rain tank do I need.
- Know how dirty the rainwater may be and how clean it is needed for use.
- Using rainwater harvesting to water a lawn or decorative landscape does not usually need to be any cleaner than having debris removed by screen filters. Rainwater that will be collected for drinking or used in equipment, will require filtration and/or treatment to potable or near-potable quality.
- Use rain harvesting accessories to keep debris such as plant and animal materials out of the water tank.
- This improves the cleanliness and health of both the container and water and will also reduce how much maintenance is needed.
- Consider adding gutter guards or gutter mesh to the roof’s gutter system.
- Gutter guards help keep debris out of the rain collection system and helps keep everything cleaner, meaning less maintenance.
- Use a tank screen if the manway on top of the tank is used to collect water inflow.
- A tank screen not only keeps debris out of the tank but also keeps pests from being able to reach water in the tank.
- Always keep the lid closed, tight and secure if a water inlet other than the manway is used, such as direct plumbing.
- This will help limit sunlight and prevent pest access. In these cases, also include a means to vent the container such as a self-venting lid or overflow port.
- Tap the water storage tank at least 6 inches above the base of the tank.
- Install an outlet, hose bib, or distribution plumbing at least 6 inches from the tank base to avoid drawing water from the sediment layer and anaerobic zone. Most rainwater containers that are pre-plumbed with a bottom outlet are already made this way.
- Consider whether a first flush device or setup is needed.
- While not always needed, a first flush diverter (roof washer, standpipe) is recommended because it helps to keep the rainwater and container cleaner over time.
- Consider using a calming device for rainwater as it flows into the tank.
- This can be either an upward-curved inlet pipe or an accessory such as a solar shield for the manway. Calming the incoming water during rain events will help to prevent disturbing the bottom anaerobic zone and remixing of any sediment that previously settled.
- Use a tank overflow kit and plumbing to prevent the tank from overflowing at the inlet, lid or manway when the container is full.
- Overflowing can cause puddling on the tank surface, at the tank screen, and around the tank base, which can attract wildlife that can add unwanted contaminants to the stored water.
- Correctly install overflow plumbing and direct extra water away from the tank base and structures.
- This will prevent the possibility for erosion of the foundation and earth around the rain container. A lot of erosion over time can make a rainwater container unstable.
- Choose an overflow design to either skim excess rainwater from the surface or discard water from the bottom of the storage tank.
- Skimming water from the surface will help remove any floating debris small enough to pass through screens. Removing water from the bottom will help remove contaminants such as sediments.
- Place rainwater collection containers in a location that gets little direct sunlight, if possible.
- This will help reduce the effects sunlight has on the container and stored water, such as algal growth. Consider our post on how to reduce algae for tips and ideas.
- Consider trimming back growing vegetation (e.g., trees) that hang over the catchment area.
- This will limit the amount of plant material debris on the roof and gutters and can also discourage animal activity.
- Consider using a floating pump that can be installed inside the container when a pump is needed to pressurize the rainwater for use.
- A floating pump, also known as a submersible or vertical pump, draws water just beneath the surface, providing the best quality rainwater from the cistern. They are especially recommended in clean water and potable water use applications
- Consider including a rain garden with a rainwater harvesting system to aid in water conservation efforts.
- Rain gardens can improve the natural irrigation ability of a landscape as well as provide a location for overflow water, both improving water conservation and potentially limiting the amount of irrigation needed.
- Know whether a municipal water connection to the tank will be needed to maintain a minimum water level.
- This is mostly applicable with in-home applications.
- Consider nearby human activity such as agricultural spraying of pesticides, etc. and industrial, manufacturing exhaust and its possible effect on rainwater quality for your use and whether purification will be needed.
- Typically only relevant for potable and indoor applications.
- Only use rainwater for potable applications (e.g. drinking, cooking) when water treatment equipment is included such as multi-stage filtration, UV light treatment, and/or chemical disinfection.
- For more on this, see our post on how to turn rainwater into drinking water.
Don’t
- Do not use clear, entirely translucent plastic containers for regular, repeat collection and use of rainwater.
- This recommendation is simply because clear water containers can be prone to high levels of algae with sunlight exposure. Algal growth is an unwanted condition that can affect water quality, clog piping, hoses, or equipment and will increase the amount of maintenance.
- Do not use any container for rainwater harvesting that was previously used to store chemicals.
- Many chemicals and materials can get absorbed into a container and release out again into water over time, even if the container is washed and cleaned many times. Brand new, ANSI/NSF 61 certified rain tanks or IBC totes that are new or rebottled are recommended for rainwater harvesting.
- Do not drink rainwater collected from a roof unless it has been properly treated (disinfected/sanitized) against potentially harmful microorganisms.
- While rainwater is fairly clean, rain can collect dirt, dust, and filth such as animal fecal matter as it flows over a roof and through gutters. This can be a source of bacteria, parasites, and sometimes viruses that can cause illness. For more on this, see our post on why should I not drink rainwater before treating it.
- Do not use rainwater to perform a final rinse on clean fruit and produce for eating.
- This is considered a potable water use and should be done only with municipal water or properly treated rainwater.
- Do not use rain barrels or tanks that remain open to the environment.
- Open water containers can become breeding grounds for insects and pests such as mosquitoes. An open container can also be contaminated by rodents and other small animals. Mosquitoes and rodents are sometimes referred to as vectors by government and other authorities.
- Do not allow rainwater overflow to drain at the tank base or at the foundation of any other structure.
- Concentrated water flow to the same place consistently over time can cause significant erosion and even damage to susceptible structures.
- Do not disturb the bottom six (6) inches of water in a storage tank.
- This area is referred to as the sediment layer, the anaerobic zone, and biofilm region. It is this area where unfiltered materials and microbiological activity can be found and are most prevalent.
- Do not neglect the recommendations and guidelines for proper installation, setup, and maintenance of rain barrels and rainwater tanks.
- Proper care of a rainwater harvesting system ensures it continues to operate well with limited problems.
- Do not use copper piping to distribute and handle rainwater in harvesting systems and in-home applications.
- The soft, slightly acidic quality of rainwater can cause damage to copper pipe over time and lead to developing pinhole leaks.
- Do not connect a rainwater plumbing system to the municipal system or supply lines without including a backflow prevention valve.
- This prevents contamination of the mains by your personal rainwater harvesting system. Backflow prevention valves can be known as a reduced pressure zone (RPZ) backflow assembly or valve. Their installation often needs performed by a licensed professional, so always first check with your local government and/or water department prior to any work.
