How to Clean Your Undersink RO Bladder Storage Tank

How Undersink RO Storage Tanks Work

Your undersink RO system includes a small pressurized storage tank (3.2 gallons) that holds filtered water ready for use. Inside the tank, a flexible bladder separates your purified water from a cushion of compressed air. When you open your RO faucet, the air pressure pushes water out of the bladder, no pump required.

Because the bladder is permanently sealed inside the tank, you cannot open it for manual scrubbing or inspection. Cleaning must be done by flushing and circulating sanitizing solution through the system.

When to Clean Your Tank

Clean your undersink RO storage tank in these situations:

Annual maintenance – At minimum, sanitize yearly or when you replace filters
After filter or membrane replacement – Good practice to sanitize the entire system
Taste or odor changes – Stale, plastic, or off-flavors in your RO water
Reduced water flow – May indicate sediment buildup or bladder issues
Extended non-use – If the system sat unused for 2+ weeks

Supplies Needed

Unscented household bleach
Measuring spoon (tablespoon)
Small funnel (optional)
Clean towel
Chlorine test strips (optional)

Step-by-Step Cleaning Process

Step 1: Shut Off the Water Supply

Turn off the cold water supply valve feeding your RO system (usually located under the sink).

Step 2: Drain the Storage Tank

Open your RO faucet and let it run until the flow stops completely. This may take several minutes. The tank is empty when water slows to a trickle and stops.

Step 3: Remove RO Filters (Optional but Recommended)

If you're due for filter replacement, remove the pre-filters, post-filter, and RO membrane now. This prevents the sanitizing solution from damaging the membrane or being absorbed by carbon filters.

If filters are new, you can leave them in place but use a weaker solution (1 teaspoon bleach instead of 1 tablespoon).

We suggest removing all filters and membranes.

Step 4: Add Sanitizing Solution

Locate the first filter housing (sediment pre-filter). With the cartridge removed:

Pour 1 tablespoon of unscented bleach into the empty housing
Reinstall the housing (without the filter cartridge)

Alternatively, disconnect the tubing at the tank inlet and use a funnel to add the bleach solution directly.

Step 5: Fill the Tank with Sanitized Water

Turn the water supply back on. The system will fill, drawing the bleach solution into the tank. Wait until the tank is full (typically 15-30 minutes for a 3-gallon tank, you'll hear the system stop producing water).

Step 6: Allow Contact Time

Let the sanitizing solution sit in the tank for 30 minutes minimum, 2 hours maximum. Do not exceed 2 hours, as prolonged chlorine exposure can degrade the bladder.

Step 7: Drain and Flush

Open the RO faucet and drain the entire tank
Let the tank refill
Drain again
Repeat until no chlorine odor remains (typically 2-3 full tank cycles)

Use chlorine test strips to verify if unsure, residual chlorine should be below 0.5 ppm.

Step 8: Install Fresh Filters

Install new pre-filters, post-filter, and membrane (if replaced). Make sure all housings are seated properly with no leaks.

Step 9: Final Flush

Discard the first full tank of water after installing new filters to flush any carbon fines or residual sanitizer.

When to Replace vs. Clean

Signs Your Tank Needs Replacement

Waterlogged tank – Tank feels constantly heavy; water pressure cycles rapidly on and off; very slow flow from faucet. This may mean that the bladder has failed.
Persistent bad taste or odor – Rubber or plastic taste that doesn't improve after sanitization
Low pressure – Tank doesn't deliver water with adequate force even when full
Age – Tanks older than 7–10 years may consider replacement regardless of condition
Visible damage – Rust, corrosion, dents, or leaks

Cleaning Is Sufficient When

Tank maintains normal pressure and flow
Water quality issues resolve after flushing
Tank is within expected lifespan
Pre-charge pressure holds steady (check annually)

Checking Tank Pre-Charge Pressure

If your tank seems waterlogged or flow is weak, check the air pre-charge:

Shut off feed water and drain the tank completely
Locate the air valve on top or bottom of the tank (looks like a tire valve)
Use a low-pressure tire gauge to check pressure
Should read 5-7 PSI when empty (reference your manual for exact pressure)
Add air with a bicycle pump if low; release air if high
If pressure won't hold, the bladder may have failed—replace the tank, or contact Crystal Quest for further troubleshooting

Safety Precautions

Use only unscented household bleach
Never exceed recommended bleach concentration
Do not leave chlorine solution in tank longer than 2 hours
Flush thoroughly before drinking water from the system
Wear gloves if you have sensitive skin

When to Call a Professional

Contact Crystal Quest support if:

You do not feel comfortable sanitizing your system and want additional details
Tank won't hold pressure after adding air
Water quality issues persist after cleaning
You're unsure how to disconnect or reassemble components
The tank is leaking or visibly damaged