Proper, regular maintenance is an important part in caring for and maximizing the service life of any piece of equipment. Water storage tanks are no exclusion from this fundamental concept, especially those intended for potable, drinking water scenarios. In this Poly Tank Series post, we will explore the details of cleaning water storage tanks and will cover why, when and how they should be correctly cleaned.
Why Do I Need to Clean My Water Storage Tank
First, why should we clean a water storage tank? The purpose of cleaning is to effectively wash, scrub, and disinfect the water tank to remove any bacteria, algae and/or silt that may have accumulated over time. Whether they are small 100 gallon rain barrel tanks or bulk 15,000 gallon vertical water tanks, cleaning a water storage tank is important to ensure it continues to operate as desired or will be ready for use when needed. Keeping the tank clean helps to maintain the total water quality so it will remain suitable for its intended application. This is a key consideration with potable water tanks.
Water tank cleaning and maintenance helps to maximize the tank’s total service life and can help identify any potential problems before they occur. Unless the tank will be completely neglected, (which eventually won’t make for very high quality water for use), it is best to perform cleaning activities regularly to make light work now rather than heavy work later.
The recommendations and methods outlined in this post are also good for most of the different types of water tanks, which includes:
- Portable Water Tanks
- Water IBC Totes
- Rainwater Collection Tanks
- Emergency Water Tanks
- Conical Water Tanks
- Stock Tanks
- RV Tanks
- Marine Tanks
When to Clean a Water Storage Tank
A regular maintenance schedule is always a good idea for any equipment, machinery or working system, so when should a water storage tank be cleaned? As part of recurring maintenance, water tanks are generally recommended to be cleaned at least once a year. This recommendation can vary based on the design specifics of the water tank, its location, extent of use, as well as changes or events within the environment.
If the tank is light in color, such as white, the frequency of tank cleaning can increase. If the tank is located in direct sunlight and outside, this can also cause tank cleaning frequency to increase. Dark colored tanks placed out of the sun will require the least maintenance and may only need cleaning once every two years. Water tanks kept or used in cooler environments will not need cleaning as often compared to those in warmer or tropical locations.
Additional circumstances can prompt when it’s time to clean your water storage tank.
- If a water quality test returns positive for E. coli or total coliform bacteria, then it’s time to clean and disinfect the tank.
- If during normal use, the taste or odor of the water changes significantly, it can indicate spoilage or contamination and that it’s time to clean the tank.
- If visual inspection reveals unacceptable algal growth or biofilm (scum) on the interior walls of the water tank it’s time to clean the tank.
- When the tank is used in connection with well water scenarios, it is recommended to clean the tank and system whenever: a new well is installed; a seasonal well is started up; well flooding has occurred; repairs to a well casing or pump have been performed, or when contamination of a well is suspected, such as due to a cracked cover.
How to Clean a Water Storage Tank
What is the recommended method for cleaning a water storage tank? Cleaning a water tank does not have to sound like a strenuous or daunting task. In fact, there is a fairly simple guideline and practice that is recommended. If the water in the storage tank will not be used as potable water for consumption, then only the first two steps are necessary. To effectively clean a water tank, follow these five steps: (1) Drain; (2) Clean; (3) Disinfect; (4) Test, and (5) Repeat, if needed.
More details on these steps are provided below.
Step 1: Drain – Completely drain the tank. With large volumes, do so appropriately. Do not discharge in a manner that is against any local regulations, that will cause damage to property or disrupt the local environment. Use the drain port located at the bottom or at true bottom found on many rainwater storage tanks rather than the outlet valve. Draining to a storm drain is preferred if available. If tipping cannot be performed to achieve full drainage in some tanks, a wet vacuum or other means can be used to fully remove all old water from the tank. This old water may be the source of why the tank needed cleaning: make sure it is drained.
Step 2: Clean – When fully drained, use soapy water and a non-metallic bristle brush to scrub the interior of the storage tank. Preferably, use an extendable brush with an adjustable head to accommodate reach into corners. Never enter larger volume tanks. Power washers are considered excellent tools for this step of the water tank cleaning process. Use a cleaning solution and necessary tools to completely clean the water tank.
A liquid soap or mild detergent mixed in water is many times a sufficient cleaning solution. Household bleach or baking soda can be used in the cleaning process for stubborn algae, biofilm or silt spots. Bleach and other cleaning products often list the proper amounts to use for cleaning, which can vary on the exact product and formulation. After cleaning, the tank should be rinsed and drained entirely 2 to 3 times to ensure all cleaning chemicals are gone.
On the topic of entering a water tank. Entering a tank should not be performed for any reason as it can be hazardous to health, especially if bleach is being used. Storage tanks are considered a confined space and entering should only be performed by professionals aware of the risks and protected against the potential hazards.
Step 3: Disinfect – Tank disinfection means to treat water that is put back into the water tank so it is safe for drinking. If the water is not for consumption, this step is not needed. Water tank disinfection involves the use of either NSF 60 approved consumer bleach (sodium hypochlorite at 5.25% chlorine content) or aqueous sodium hypochlorite. The amount of chemical needed to disinfect will depend on the concentration strength of the product. Some products may provide this information for the consumer.
To disinfect water in a storage tank with household bleach at 5.25% sodium hypochlorite strength: fill the container with 1 ounce of liquid bleach for every 60 gallons of water – the equivalent of 0.5 milliliters of bleach for every 1 gallon of water. Let the water stand at least 30 minutes before use.
Step 4: Test – After disinfection, water stored within the water tank should be tested to make sure it is free of coliform bacteria such as E. coli and that chlorine values are below safe levels. This verifies that cleaning was successful, and again, if the water is not intended for consumption, this step is not needed. Various modern methods and means exist for testing the water for potential contamination. Test strips exist that can demonstrate the general range of detected chlorine and whether specific bacteria are present. However, analytical laboratory tests are the most accurate and provide the most guarantee that the water is safe for use and consumption.
Step 5: Repeat – If the results of the test indicate bacteria remain, the complete process should be repeated. Adding more disinfectant may also be sufficient. If residual chlorine or bleach smell remains, simply allow more time to pass and the chemical to dissipate to the appropriate levels prior to use or consumption.
Cleaning Very Large Water Tanks
Whenever cleaning and disinfecting very large tanks associated with water storage facilities, businesses or industries under federal or state oversight, the requirements outlined in AWWA C652 would apply and should be followed.
Takeaway | How to Clean a Water Storage Tank
Unless you want the quality of your stored water resources to diminish over time, regular cleaning and maintenance will be required for a water tank. Depending on the size of the tank and amount of work, the amount of time it takes to clean the tank can range from an hour or two, to a full day or multi-day event, so plan your uses and any associated services accordingly. Know the method and steps involved in cleaning your water storage tank and get on a regular schedule so this recurring task can be repeated as needed and with minimal effort.