RO storage tank cleaning: why it matters and how often

The membrane makes clean water. Then that water sits in a plastic tank, at room temperature, for hours or days. Clean water in a warm dark tank is exactly what biofilm likes.

What builds up

A thin slippery layer on the inside of the tank — bacteria and the film they live in. It is not dramatic and it is not usually dangerous, but it is why RO water sometimes tastes musty, and it is the reason the post-carbon filter exists.

How often

Every six months is a sound interval. Every three if the RO is used lightly, because water that sits longer grows more.

The signs

• Musty or earthy taste that a new post-carbon filter does not fix
• A slimy feel inside the tank if you reach in
• A smell when the tank lid is lifted
• Small dark specks in the water after the RO has been idle

What a proper clean is

Tank drained fully, inside scrubbed with a food-safe sanitiser, rinsed thoroughly, refilled and the first fill discarded. The float valve and outlet are cleaned at the same time. If the tank is old and scratched inside, it may be time to replace it — scratches hold film.

Do not use bleach or dish soap in the tank. Both leave residue that taints the water for days. Use a food-grade sanitiser or ask the technician to do it as part of the service.

Pairing it with a service

Tank cleaning fits naturally into the six-monthly filter visit. Ask for it. It adds a few minutes and removes the most common cause of 'the water tastes off but the filters are new'.