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Yes, you can clean some water tanks yourself, but only if you can do the job without climbing or crawling inside the tank.
Small rain barrels, accessible above-ground tanks, and some IBC totes are often reasonable DIY cleaning jobs. Large cisterns, underground tanks, and tanks that require a person to enter should be handled by trained professionals. A tank can become a dangerous confined space because it may have poor ventilation, a difficult exit, slippery surfaces, or other hazards. OSHA specifically identifies tanks as spaces that can meet the definition of a confined space.
The cleaning method also depends on what you use the water for. A tank used only for garden irrigation does not have the same water-quality requirements as a tank supplying household or drinking water.
When You Can Usually Clean a Water Tank Yourself
DIY cleaning is most practical when the tank is above ground and you can reach the areas that need cleaning from outside.
Typical examples include:
- Rain barrels with removable lids
- Small garden-water tanks
- Accessible IBC totes
- Above-ground rainwater tanks with large inspection openings
- Tanks that can be fully drained without entering them
You should be able to drain the tank, remove sediment, wash accessible surfaces, rinse it, and inspect the fittings while remaining outside.
If cleaning requires your head, shoulders, or whole body to pass through the tank opening, treat it as a different type of job. Do not assume an empty tank is safe to enter.
When You Should Not Clean the Tank Yourself
Hire a qualified tank-cleaning professional when the work involves entering the tank.
This is especially important for:
- Underground cisterns
- Large concrete tanks
- Tall vertical tanks
- Tanks with narrow access openings
- Tanks with difficult ladders or exits
- Tanks connected to electrical pumps or controls that cannot be safely isolated
- Tanks that previously held chemicals, fuel, sewage, or unknown materials
- Tanks with serious structural damage
A large empty tank can still have dangerous conditions. Limited ventilation, slippery surfaces, electrical hazards, and difficult rescue access can all be problems. OSHA guidance warns that tanks with restricted entry and serious physical or atmospheric hazards may require confined-space safety procedures.
Having another person standing outside does not automatically make tank entry safe.
How to Clean an Accessible Rainwater Tank
For a simple above-ground rainwater tank, the basic process is to stop incoming water, drain the tank, remove sediment, clean accessible surfaces, rinse, and put the system back into service.
1. Stop New Water From Entering
Disconnect or divert the downspout or inlet before starting.
You do not want a sudden rainstorm sending roof runoff into an open tank while you are working.
Also make sure the overflow route remains safe. Water should not be redirected toward foundations, electrical equipment, or areas where it could cause erosion.
2. Shut Down Pumps and Electrical Equipment
If the tank supplies a pump, turn the system off before draining or cleaning.
A pump that continues running as the water level drops can run dry. Depending on the pump design, dry running may damage it.
Do not work on electrical wiring or submerged electrical equipment unless you are qualified to do so. Water and electrical work are a poor DIY combination.
3. Drain the Tank
Use the normal drain or outlet when possible.
Plan where the water will go before opening the valve. A large tank can release a surprising amount of water. Avoid flooding buildings, neighboring property, septic areas, or unstable ground.
You may not need to waste all the stored water. If the water is suitable for irrigation, you may be able to use much of it on the garden before cleaning day.
4. Remove Bottom Sediment
Most rainwater tanks eventually collect some sediment.
This material may include:
- Fine roof dust
- Pollen
- Small pieces of leaves
- Insect material
- Organic debris that passed through screens
- Particles that settled out of the stored water
Remove as much loose material as you can from outside the tank.
A tank with a bottom drain may allow much of the sediment to flush out. Accessible tanks may also allow sediment to be removed through an inspection opening using tools designed to reach inside without requiring a person to enter.
Avoid creating a situation where you feel tempted to climb inside just to reach the last bit of dirt.
5. Wash Accessible Surfaces
Use clean tools that will not damage the tank.
A soft or medium brush may be enough for slime or deposits that can be safely reached through the opening. Follow the tank manufacturer's instructions if they specify approved cleaners.
Avoid harsh solvents or household chemicals that could damage plastic, seals, coatings, or fittings.
If you use a cleaning agent, rinse it out thoroughly before returning the tank to service.
6. Check the Tank While It Is Empty
An empty tank gives you a useful chance to inspect parts that are normally difficult to see.
Check accessible areas for:
- Cracks
- Loose fittings
- Damaged seals
- Leaking bulkhead fittings
- Blocked drains
- Damaged inlet screens
- Overflow problems
- Insect entry points
A bulkhead fitting is the fitting that passes through the tank wall and creates a sealed connection for a pipe or valve.
Do not overtighten plastic fittings while inspecting them. Excess force can distort seals or crack the tank wall.
7. Rinse and Drain Again
Rinse away loosened sediment and cleaning residue.
Keep rinsing until the remaining water is reasonably clear and there is no visible cleaning residue.
Cleaning removes dirt. Sanitizing is a separate step when sanitation is required.
CDC guidance for drinking-water storage containers, for example, separates washing from sanitizing rather than treating the two as the same process.
Does a Rainwater Tank Need to Be Disinfected?
Not every tank needs the same sanitation process.
For a tank supplying drip irrigation or general garden water, removing accumulated organic material may be the main goal.
A tank used for drinking water is different.
Do not assume that scrubbing or adding bleach automatically makes collected rainwater safe to drink. Roof runoff can pick up microorganisms, animal waste, chemicals, metals, roofing materials, and other contaminants before the water ever reaches the tank.
Drinking-water use needs to be considered as a complete system, including suitable collection surfaces, debris control, treatment, maintenance, and current laboratory testing where appropriate.
If a tank is part of a potable water system, follow the tank manufacturer's instructions and applicable local health requirements for cleaning and disinfection. Potable means suitable for drinking.
For large potable-water tanks, professional cleaning and sanitation is often the safer choice.
Be Careful With Bleach and Other Disinfectants
Chlorine can be useful for sanitizing appropriate water-storage equipment, but more is not automatically better.
CDC provides specific bleach concentrations for sanitizing small drinking-water storage containers. Those directions should not simply be scaled up and treated as a universal recipe for every large cistern or rainwater system.
Guidance on simple water-tank cleaning methods helps evaluate safe ventilation and overflow routing for stored water.
Tank material, water volume, intended use, chlorine concentration, contact time, and local requirements can all matter.
Never mix chlorine bleach with ammonia, acids, vinegar, or other cleaners.
If you have a large potable tank and are unsure how it should be disinfected, use qualified professional guidance rather than improvising a chemical treatment.
How Often Should You Clean a Rainwater Tank?
There is no single cleaning interval that fits every system.
How quickly sediment builds depends on the entire collection system.
A tank may need attention sooner if you have:
- Trees over the roof
- Heavy pollen
- Frequent leaf debris
- Poor gutter screens
- Dirty gutters
- An ineffective first-flush system
- An uncovered or poorly screened inlet
- Visible sediment accumulating on the bottom
A first flush is a device or arrangement that diverts some of the first roof runoff from a rain event. That first runoff often carries a higher load of loose dirt and debris from the roof.
Good upstream maintenance can greatly reduce how much material reaches the tank.
Instead of cleaning by the calendar alone, inspect the system periodically and watch sediment levels, screens, gutters, inlets, and water condition.
Cleaning the Tank Is Only Part of Maintenance
If a rainwater tank becomes dirty quickly after cleaning, the real problem may be upstream.
Check the whole path from roof to tank.
Roof and Gutters
Keep gutters and accessible roof-drainage areas free of heavy leaf buildup.
Do not take unnecessary risks working on a roof. Use professional help when safe access is uncertain.
Leaf Screens
Clean screens before they become clogged.
A blocked screen can reduce collection and cause water to spill where it should not.
First-Flush Device
If your system has one, clean and reset it according to its design.
A first-flush chamber that stays full of old water or debris may not work as intended.
Tank Inlet
Make sure the inlet prevents large debris and insects from easily entering the tank.
Overflow
Keep the overflow clear and properly screened where appropriate.
A blocked overflow can cause water to back up or escape from unintended places.
Pump Intake
If the tank feeds a pump, inspect accessible strainers or prefilters according to the equipment instructions.
Heavy sediment near the pump intake can contribute to clogging and poor performance.
What About Algae Inside the Tank?
Visible algae usually means light is reaching stored water.
Simply cleaning the algae may not solve the cause.
Check for:
- Transparent or lightly colored tank walls
- An uncovered inspection opening
- Light entering around the lid
- Clear pipe sections exposed to sunlight
Rainwater storage usually performs better when stored water is protected from sunlight.
Do not repeatedly add algaecides or other chemicals without confirming that they are appropriate for the tank material and intended water use.
What If the Water Smells Bad?
Odors can come from organic material decomposing in the tank, but smell alone cannot tell you whether the water is safe.
Start by checking for obvious problems such as:
- Leaves entering the tank
- Dead insects or animals
- Stagnant first-flush water
- Heavy bottom sediment
- Blocked screens
- Dirty gutters
- Cross-connections with another water source
For irrigation water, cleaning the tank and fixing the debris source may solve the problem.
If the water is used for drinking or other household purposes where people can ingest it, do not rely on appearance, taste, or smell as a safety test. Investigate the whole system and use appropriate water testing and treatment.
The Simple DIY Rule
A useful rule is:
If you can drain, inspect, and clean the tank while staying safely outside it, the job may be suitable for DIY maintenance. If you need to enter the tank, stop and use a qualified professional.
The goal is not to make the inside look perfectly new. The goal is to remove accumulated material, keep the collection system working properly, and avoid introducing new contamination or creating a safety hazard.
Frequently Asked Questions
Can I climb inside an empty water tank to clean it?
You should not treat an empty tank as safe to enter. Large tanks can have limited exits, poor ventilation, slippery surfaces, and other confined-space hazards. Use trained professional help when cleaning requires tank entry.
Can I pressure wash the inside of my water tank?
Some tank materials may tolerate suitable pressure-cleaning methods, while others can be damaged. Follow the tank manufacturer's instructions. Do not enter a tank with a pressure washer simply because deposits are difficult to reach.
Can I use bleach to clean my water tank?
Bleach can be used in some sanitation procedures, but the correct method depends on the tank, water use, bleach concentration, and applicable guidance. Do not improvise a large-tank dosage, and never mix bleach with other cleaners such as ammonia or acids.
Do I have to empty the whole tank?
A thorough bottom cleaning normally requires lowering the water enough to remove accumulated sediment. Tanks with good drains may be easier to flush without manual cleaning. The exact method depends on the tank design and the amount of buildup.
How do I keep my rainwater tank cleaner?
Keep gutters and inlet screens maintained, reduce leaf entry, maintain the first-flush system if you have one, keep insects out, and prevent sunlight from reaching stored water. These measures reduce the amount of material that reaches the tank.
Is rainwater safe to drink after I clean the tank?
Not necessarily. Cleaning a tank removes dirt and sediment but does not establish that roof-collected rainwater is potable. Drinking-water use requires suitable collection, treatment, maintenance, and appropriate testing, along with any applicable local requirements.
Can I clean an IBC tote myself?
Often, yes, if you know what the tote previously contained and can clean it safely from outside. Do not use a tote that previously held toxic chemicals for drinking-water storage. CDC also advises against using drinking-water containers that previously held toxic substances.
