Whether you are collecting rainwater for your household water supply or having water trucked in to fill your water tank, regular maintenance of your cistern is vital to your home's overall water quality. Below are recommendations we give our customers based on our years of field experience.
How often should I clean my cistern or water tank?
Our general rule of thumb is that a rain-fed, below-ground cistern should be cleaned once every 10 years. However, the frequency depends on the quality of the installation. If good quality roof washers were used — like our Wisy Vortex filter or Monjolin filters — and if the cistern is well-sealed with no potential for dirt, mud, or rodents to get in, then you're looking at closer to 20 years between cleanings.
If the installation was not done well and you have a source of mud or dirt getting in, or rodent activity inside your tank, the cistern needs to be cleaned right away and properly evaluated and sealed.
If you suspect your cistern is leaking, that is also a great time to clean the tank, evaluate, and re-seal it. For instructions on how to waterproof your water tank, see our video: How to stop a cistern water tank from leaking the RIGHT WAY.
Pre-filtration and roof washers are absolutely crucial for maintaining great water quality inside your tank. It is far easier to pre-filter the water and maintain those pre-filters than it is to clean the cistern. If you don't have good pre-filtration, at minimum install something basic to keep shingle grit and leaves out of your tank. Install the pre-filters, clean the cistern, and then return to the 10-year cleaning schedule.
What other steps are needed for cistern maintenance?
In addition to cleaning your cistern every 10 years, it is important to regularly disinfect it. This can be accomplished one of two ways:
- Chlorine tablets — Add a small amount of slow-dissolve, NSF-approved chlorine tablets to your cistern. We recommend adding a small handful (enough to cover your palm) every 3 months directly to your cistern. Wear gloves when handling chlorine pellets.
- Ozone generator — Regularly use an ozone generator to pump O3 into your cistern. Ozone creates an environment where bacteria cannot survive, helps clarify the water, and clears up odors. For a maintenance dose, an ozone generator only needs to run 2–4 hours per week (assuming continuous disinfection filtration inside the home). Ozone naturally dissipates, leaving no harmful additives in your water supply. Note: ozone generators must be used with outdoor tanks only, and can only pump into 4 ft. of water — suspend the airstone accordingly. See our video: Easy and Affordable Rain Purification - How to Install an Ozone Generator on Cistern.
How to clean your cistern or water tank
Once you've determined that your cistern needs to be cleaned, here's what you'll need:
- A minimum of 2 people
- Flat, clean shovel
- Ladder
- Air exchange/ventilation fan
- Respirator with activated carbon filter
- Earplugs
- Gloves
- Protective eyewear
- Headlamp
- Large-capacity pump
- Small transfer/utility pump
- Buckets
- Rope with hook
- Wet/dry vacuum
- Pressure washer
- Unscented bleach
- Barrel (minimum 50-gallon)
- Turn off power to your pump and close the main valve in your house. This ensures you don't lose prime in your pump as you drain the tank.
- Fill a barrel by pumping water from the top of the cistern. Place the barrel close to the cistern. As it fills, pour in one quart of unscented bleach — this barrel will supply water to your pressure washer.
- Pump out the cistern. When possible, stir up the water inside to allow the pump to discharge some of the sedimentation.
- Ventilate. Once the large-capacity pump can no longer remove water, begin circulating fresh air into the cistern with the ventilation fan. Suit up with your respirator, gloves, safety glasses, and earplugs.
- Pressure wash the walls. When safe to enter, gravity-feed the barrel to the pressure washer. Be careful not to use too strong a jet — sealant on concrete tanks can break off.
- Remove remaining water and debris. Use the utility pump to evacuate as much remaining water as possible. Shovel debris into buckets and have your helper hoist them up. Finish with the wet-vac to clean up remaining sludge and buildup.
If this sounds too daunting and you're within 2 hours of our shop in Yellow Springs, Ohio, call or text us at (937) 949-1100, or fill out a service request form — we'd be happy to provide a quote to clean your cistern for you.
