Regular cleaning of a rainwater harvesting tank is as important as knowing how to properly clean one. Modern rainwater harvesting tanks come in a variety of shapes, sizes and manufacturing material options, but the steps to annual maintenance are relatively the same. Tank cleaning will never be the funnest of jobs, rather it’s a responsibility of tank ownership and one that should be done sooner rather than later in order to avoid a larger, more toilsome task.
If you own a rain barrel or bulk rainwater collection tank, full cleaning is recommended at least once a year. The storage tank should be inspected frequently for signs of infiltration by debris or pests, contamination in the forms of biofilms and algae, and it should be cleaned if the inspection reveals poor conditions. Engaging in this type of care will ensure the container remains in top working order and continues to capture and provide the quality rainwater resource you want for your intended applications.
Steps to Cleaning Your Rain Tank
In this Rain Tanks Series post, we will show how to clean a rainwater harvesting tank in a fairly straightforward process that can be accomplished in five (5) steps.
Step 1: Determine Time for Cleaning
Prior to cleaning the rain tank, first determine when it should be cleaned. Rainwater harvesting tanks do not have the exact same guidelines as a potable drinking water tank unless it will be used for that purpose. Therefore the cleanliness standard and requirement may vary.
- Rain Tanks for Irrigation: Rain tanks used for irrigation in watering plants, lawns and landscapes require the lowest level of cleanliness for the tank. Irrigation tanks should still be cleaned at least once a year. Infiltration by organic matter (plant debris, animal tissue, remains, and droppings) may not be harmful to irrigation purposes but beneficial to plants by providing valuable nutrients. Disinfection of the tank and/or water will not be required.
- Rain Tanks for Appliances / Equipment: Rain tanks used for appliances or work equipment require a moderate level of cleanliness. Tank infiltration by organic matter and sediments can clog system plumbing and/or affect normal equipment operation as well as running service life. Clean at least once per year or when inspection reveals it is needed. Disinfection may be required or recommended.
- Rain Tanks for Drinking, Cooking, Bathing: Rain tanks used for potable uses require the strictest level of interior tank cleanliness and water treatment. If the tank has been infiltrated by foreign matter, animals, sediments, chemicals or other particulates, cleaning and/or treating the water is likely needed. Tank cleaning and disinfection is required to achieve and maintain potable quality rainwater and should occur once a year at minimum or whenever inspection indicates it is needed.
Rainwater Pro Tip
Rainwater harvesting containers positioned in open sunlight and made of light colored material often require more frequent maintenance due to algae build up. Rain tanks placed away from sunlight and made of dark colored material are significantly more resistant to algae growth and will require cleaning maintenance less often.
Step 2: Drain the Rain Tank
This step is easier for lower capacity rain tanks. The unwanted, potentially dirty water in the rain tank needs to be drained so the tank interior can be cleaned, and drained in a manner that will be non-damaging to the surrounding environment or infrastructure. A few hundred gallons, let alone a thousand, two or more, of unclean rainwater is a significant volume to discharge.
If necessary, use a hose to displace the water and runoff accordingly or use it to water nearby vegetation. Always discharge water away from houses and other structures in a way that is safe and responsible. Depending on the total volume, draining may need to be done at several different times to allow the ground time to absorb the water.
Step 3: Clean the Empty Reservoir
With all water removed, the tank interior can now be cleaned. Use a soapy water mixture along with a coarse, non-metal bristle brush to scrub the tank walls. Use of an extendable rod with adjustable head is recommended for access in larger tanks and for difficult to reach areas. A pressure washer is a good tool that can help make light work of cleaning a rainwater harvesting tank.
Use a mild bleach (sodium hypochlorite) or baking soda (sodium bicarbonate) solution to assist in removing algae or sediment deposits stuck on interior walls. Entering a tank being cleaned with chemicals is never recommended unless proper protective equipment is worn, and even still, we cannot recommend it personally due to safety hazards. Perform final rinses with pure, clean water and allow it to drain. Ensure all soapy and unclean water is fully rinsed away – a thorough 3-times rinse is often satisfactory.
Rainwater Pro Tip
Non-potable rainwater tanks are finished at this step and can satisfactorily return to normal rainwater harvesting use. Non-potable rain tanks are clean if visual inspection indicates they are free of algae, free of silt, biofilm scum, and sediment buildup, and free of physical organic matter.
Step 4: Disinfect Tank and System (potable applications)
Disinfecting your rain harvesting tank is required if the water will be used for potable applications such as cooking, drinking or bathing. It is recommended if the rainwater will be used for appliances, toilets or other equipment.
- To disinfect a rainwater supply so it is safe to drink, use 40 mL consumer grade, NSF approved liquid bleach at 5.25% active strength for every 100 gallons of rain water. This is a direct ratio and can be modified according to your tank’s exact capacity; e.g., 100 mL for 250 gallons; 4 mL for 10 gallons; etc.
- To shock chlorinate a rainwater supply, use 1 quart consumer grade, NSF approved liquid bleach at 5.25% active strength for every 250 gallons of rain water. This is a direct ratio and can be modified according to your tank’s exact capacity; e.g. 4 quarts for 1000 gallons; 1.6 cups for 100 gallons; etc.
In step-by-step format: (1) Let the rainwater reservoir fill prior to use; (2) Add required volume of bleach; (3) Open taps to allow bleached water to fill plumbing connected to the rain tank; (4) Wait 24 to 48 hours for chlorine levels to diminish as disinfection occurs; (5) Validate water is fully disinfected and safe for use.
Step 5: Validate Tank is Clean or Repeat
If disinfection was performed, use test strips or laboratory analysis to verify that the water quality is at the desired level. If chlorine values remain high, allow more time to pass prior to use. If test results indicate bacteria is present, the cleaning and disinfection process should be repeated. A valid water quality test indicates the rain tank has been successfully cleaned.
*Rainwater Pro Tip: As an alternative to disinfecting the harvested rainwater with bleach, an ultraviolet water treatment system can be used to actively disinfect the rainwater prior to its being used.
Takeaway | Cleaning Your Rainwater Harvesting Tank
Cleaning your rainwater storage tank may be a task but it does come with its reward. In the end, it’s rewarding to know the most integral part of your rainwater harvesting system has been fully inspected, fully cleaned and returned to service. A clean rain tank is necessary for a healthy system that provides rain water at the right level of quality and not one simply supporting the abundant growth of algae.
If looking for a rainwater harvesting tank, we have one of the largest selections in terms of color, size, volume capacity and customization options offered from America’s leading tank manufacturers. We offer polyethylene rain tanks, a rain barrel, galvanized steel and stainless steel metal rainwater tanks. If you have comments or require further assistance, never hesitate to reach out to us today.
