RO water tastes different: which filter is due

Taste is the first instrument you have. It is not precise, but it narrows things down more than people expect.

Salty or mineral

Dissolved solids are getting through. The membrane is worn, or a bypass valve is letting untreated water mix in. A TDS meter confirms it — if the number has climbed well above where it used to sit, the membrane is done.

Flat or lifeless

The opposite problem. A mineraliser cartridge, if fitted, is spent, or the TDS controller has drifted too low. Water with almost nothing in it tastes strangely empty.

Plasticky or chemical

The post-carbon filter is exhausted and no longer polishing the taste, or a new filter was not flushed properly after fitting. Run the tap for a few minutes; if it clears, it was the flush.

Musty or earthy

Biofilm in the storage tank, or a carbon filter left in far too long. The tank needs cleaning and the filter changing. If it comes back quickly, the UV lamp is not working.

Slightly sweet

Usually fine — some carbon filters give this for a week when new. If it persists, a sediment filter is breaking down.

A sudden strong change in taste, especially chemical, means stop drinking it until it is checked. Gradual drift is a filter; sudden change is a fault.

What the visit does

TDS measured at the inlet, after the membrane and at the tap. Each stage inspected. The one that is spent is changed; the ones that are fine are left. You are told which is which.