Why Does My RO Water Taste Bitter or Salty? (Delhi, 2026)

Before you call anyone: three checks that cost nothing

All three are free and between them they place the problem inside the machine, inside the tank, or outside the flat entirely. Do them before you agree to any part.

• 1. Taste the water going in. Fill a glass from the tap or line that feeds the purifier and taste that. If the input already tastes salty or bitter and the output tastes like a weaker version of it, the membrane is the suspect. If the input tastes as it always did and only the RO tap has changed, the fault is downstream, in the machine or its tank.
• 2. Take a TDS reading in and out. This is the one that settles it. Dip the meter in a glass of the input water, note the number; do the same with a glass from the RO tap, note that number. A working system produces a large gap between the two. An output number sitting close to the input number means dissolved solids are getting through. If you do not own a meter, ask the technician to take both readings in front of you and to show you the display.
• 3. Work out when it changed, and what else changed that week. Did it start after a service? After a holiday when nobody drew water for days? After a tanker delivery, a supply cut, or work on a street main nearby? Ask a neighbour on the same line whether their water tastes different too. A yes from the neighbour moves the whole investigation outside your flat.

Those three answers — input taste, the two TDS numbers, and the timing — are what a good technician wants anyway. Having them ready is the difference between a targeted visit and a guessing one.

A tired membrane: when the output starts tasting like the input

This is the commonest cause of a salty or heavy taste, and the TDS pair proves it.

The membrane is the fine barrier that holds back dissolved salts. Everything upstream of it — sediment, carbon — exists to protect it. Over months it fouls, and on hard NCR groundwater it fouls faster; eventually it stops rejecting what it used to reject, and the water it produces drifts back toward the composition of the water going in. You taste that drift before any warning light tells you about it: crisp becomes flat, then heavy, then frankly salty.

• What it looks like. A gradual change over weeks rather than a change overnight. Often accompanied by a slower fill as the same membrane struggles.
• How to confirm it. Two TDS readings, input and output, taken minutes apart. If the output is close to the input, the membrane is spent, damaged, or being bypassed. A large gap means the membrane is fine and the taste is coming from somewhere else on this page.
• The bypass case worth knowing. Some machines blend a little untreated water back in, or fit an adjustable valve for it, precisely so the output does not come out too flat. If that blend has been set wide open — sometimes at a previous service — the output TDS jumps and the taste turns, with a perfectly sound membrane inside. Ask specifically whether a blend or bypass valve is fitted and how it is set before anyone condemns the membrane.
• DIY? No. Membrane work means opening a pressurised housing. It is a technician job, and it should follow a reading, not a hunch.

If a replacement genuinely is due, what drives membrane replacement cost and when a change is actually due will help you judge the quote.

A spent carbon filter, or a tank that needs cleaning out

If the TDS gap is wide, the membrane is doing its job and the taste is coming from one of the cheaper stages, or from where the water sits.

• An exhausted carbon filter. Activated carbon is what removes the chlorine note and the general "off" edge from the water. Its capacity is finite and, when it is used up, it does not fail loudly — it simply stops adsorbing, and the tastes it used to take out start coming through again. People describe the result as bitter, chemical, or medicinal. How to confirm: compare with the input water — if the input has that same note and the output now shares it, the carbon stage is the reason. What it is: a routine cartridge change, not a major repair, and it is worth doing promptly because a dead pre-carbon also stops protecting the membrane.
• A storage tank that needs sanitising. Water that sits still develops a stale, musty or slightly earthy taste, and the inside walls of a neglected tank build up a soft film that keeps contributing it even after the water is changed. How to confirm: the taste is strongest on the first glass of the day or after a few days away, and improves after you have drawn off a lot of water. What to do: drain the tank fully, let it refill and taste again; if it returns, the tank needs cleaning out properly by a technician as part of a service. The same applies at building scale — cleaning your overhead tank is often the real fix when every tap in the flat shares the taste.
• A spent post-carbon or mineral cartridge. Many units fit a final polishing stage after the membrane. When it is exhausted the water can taste flatter or sharper than you are used to. Another inexpensive cartridge, not a machine fault.

These are the cheap answers, and they are the ones to rule out first — a technician who opens with the membrane and never mentions the carbon stage is skipping the inexpensive explanation.

Very low TDS tasting flat, and a change in the water coming in

Two more causes, and neither of them is a broken part. Both catch people out because the machine is behaving exactly as designed.

• Output TDS so low the water tastes flat. Dissolved minerals are a large part of what gives water any taste at all. Strip most of them out and what is left can read as flat, “empty”, or — to some people, and this is very much a matter of individual palate — slightly bitter or metallic. It is common on a brand-new or freshly replaced membrane, because a new membrane rejects more than the tired one you had grown used to. How to confirm: a very low output TDS reading alongside a taste complaint, with everything else working normally. What to do: ask the technician about the blend or mineral stage on your model and how it is set. This is a preference to be dialled in, not a fault to be repaired, and it is worth saying so before anyone starts replacing parts.
• The water coming in has changed. This one has nothing to do with your machine. A tanker delivery instead of the mains, a borewell brought in when the line runs short, a switch of supply zone, or work on a street main can all change the taste of the input — and since the output is made from the input, the output follows. How to confirm: taste the input water; ask a neighbour on the same line; ask the RWA or the building caretaker whether the source changed this week. If the input tastes different and neighbours agree, no part in your purifier is at fault and replacing one will not change the taste.

The second case is worth taking seriously rather than shrugging at. Where the taste of the incoming supply has changed and stayed changed, the questions belong to your RWA or your water utility, and the answer belongs in a laboratory report on a sample of your own water — not in a new cartridge. Our water tastes bad or smells guide deals with supply-side taste in more detail, and discoloured tap water is the related symptom to check for at the same time.

When to call someone, and what to tell them

Call a technician when the taste has changed and stayed changed for more than a few days, when the output TDS has crept close to the input, when the change came with a slower fill, or when draining and refilling the tank makes no difference. Call sooner if the taste arrived alongside cloudy water, a new noise, or a beeping alarm, because those together usually point at one cause rather than three.

What to tell them: when the taste changed and how you would describe it (salty, bitter, flat, metallic, musty); your input and output TDS numbers if you have them; whether the input water tastes different too; whether neighbours on the same line agree; when each stage was last changed and by whom; whether a tanker or borewell has been feeding the building recently; and whether the tank has been drained and refilled since. That list gets the right cartridge on the van.

What to insist on during the visit: both TDS readings taken in front of you, before and after any work; an itemised quote with labour and each part on its own line; and the old cartridge handed to you. What is not a DIY job: the membrane, any pressurised housing, the pump, and the wiring.

For the ranges that let you judge a quote, see RO repair cost, RO service cost and TDS and membrane replacement cost. If the machine is also not working properly in other ways, start there instead. Habits that keep taste steady are in our RO and drinking water tips and, for hard-water homes, hard water home tips.