Two minutes before you open anything
Slow can mean two things, and they have different pages. If the tank is full and the stream from the tap is weak, the purifier is making water fine and the problem is between the tank and the tap: a tank outlet half shut, a kinked tube, or simply a tank that is nearly empty. If the tank is empty and takes hours to fill, or the tap only ever gives a trickle, the purifier is making water slowly. That is this page. If it is making no water at all, silence in the cabinet and nothing at the drain, go to the tank not filling guide instead, because that is a control fault, not a flow fault.
One number helps. The LUXGEN purifiers are rated at 15 litres an hour, so an 8 or 9 litre tank should fill from empty in well under an hour on fresh cartridges. Time one refill on the day the cartridges are new and write it on the housing. Then a slow purifier is a fact rather than a feeling, and you can tell whether a change fixed it.
The five causes below sit in the order the water meets them, which is also the order of cost. Work down the list and stop when the flow comes back.
Cause 1: the sediment cartridge, ₹190
The first thing the water meets is the first thing to check, and it is the cheapest part on the machine. A wound polypropylene cartridge passes about 1.9 litres a minute when new. It catches sand, rust and silt, and every gram it catches narrows the path. On borewell or tanker water it can load in six months; on municipal supply it lasts towards twelve. Past that, the pump behind it is pulling water through a cartridge that has become a plug.
Check it by looking. Close the inlet tap, open the purifier's tap to let the pressure off, unplug the machine, and unscrew the first housing. The cartridge went in white. Brown across most of its length means it is done, and a brown ring in the bowl says the same. Fit a new Universal-Fit sediment cartridge or a Branded-Fit depending on the housing, both ₹190; the fit guide tells you which, and a cartridge that does not seal is its own cause of slow flow. If there is a wall-mounted pre-filter bowl ahead of the purifier, open that first. Its candle takes the grit before the purifier does and loads sooner; the two-candle kit and the 9-inch candle are the two LUXGEN parts for it.
Run the purifier and time the refill. In most cases this is where the page ends.
Cause 2: the carbon cartridge, ₹220
If a fresh sediment cartridge did not bring the flow back, the next stage is the carbon block. It is there to take out chlorine, and it does that until it is full, but it also blocks. Silt that got past a spent or badly seated sediment cartridge lands on the block and blinds it, and a block well past its twelve months is slow whether or not the water still smells of anything. Low pressure from a blocked pre-filter can nudge the output TDS up a little, but a reading that has doubled from day one is the membrane; a reading that has barely moved while the flow has halved is a blockage ahead of it.
Replace it with the Universal-Fit carbon cartridge at ₹220 or the Branded-Fit at ₹250. If both cartridges are near a year old, change the pair together: ₹410 to ₹440, and the filter change schedule says why they fall due at the same time anyway. If chlorine has been coming through in the taste, the carbon was already exhausted and the membrane has been taking the damage; the taste guide covers that case.
Cause 3: inlet pressure, usually ₹0
A pump can only push the water it is given. If the supply to the purifier has dropped, the pump runs, the drain dribbles, and the tank takes all day. The causes are mostly free to fix.
- An overhead tank running low, or a supply that only comes at certain hours. Flow that is fine in the evening and poor at six in the morning is the supply, not the purifier.
- An inlet tap half shut after a cartridge change. Open it fully.
- A kinked or crushed quarter-inch tube between the tap and the purifier, often where it passes behind the machine or through a cupboard wall. Follow it by hand.
- A choked pre-filter bowl, already covered above, which is the same fault seen from the other side.
To check, close the inlet tap, pull the tube off the purifier's inlet into a bucket, and open the tap for a few seconds. A strong, steady stream means the supply is fine and the fault is inside the machine. A dribble means the fault is upstream. Many purifiers carry a low-pressure switch that holds the pump off when the inlet pressure falls below its setting; when the supply is weak enough to trip it, the purifier stops entirely rather than slowing, which is why that symptom lives on the tank not filling page. Never bridge the switch to make the pump run: it exists to stop the pump running dry.
Cause 4: the pump, ₹1,299
Only now the pump, and only after the sediment cartridge is fresh, because a pump starved by a blocked cartridge sounds and behaves exactly like a failing one: it whines, it runs hot, and it delivers a trickle. Replace the ₹190 part, and if the pump settles, it was never the pump.
If the cartridges are new, the supply is strong and the pump still runs with a rising whine or a rattle while the tank crawls, it is worn. The LUX-PUMP-100 is the replacement for 100 GPD systems: 24 V DC, 140 PSI, 1.5 litres a minute, ₹1,299. Two cautions. First, the adapter that feeds the pump is mains voltage in a wet cabinet, and a tired adapter can starve a good pump; testing that is a technician's job, not a homeowner's. Second, the pump has an inlet and an outlet and runs happily backwards while delivering nothing, so fitting it is on the technician side of the service vs DIY line. Buy the part at the listed price and pay for the visit. The booster pump guide has the full failure signs and the pump-to-membrane pairing.
Cause 5: the membrane, ₹650 to ₹900
The membrane comes last because it is the dearest, and because slow flow on its own almost never means the membrane. Scale and fouling on its surface do cut the flow through it, but they raise the output TDS at the same time, and that is the test. Read the feed and the output with a meter. If the output has roughly doubled from the day-one figure with the feed unchanged, and the tank is slow with fresh cartridges and a healthy pump, the membrane is done. If the output is still a few percent of the feed, it is not, however slow the tank is, and something above is still the cause. The RO output TDS guide explains the ratio and the membrane replacement guide the full test.
When it is the membrane, three fit most domestic purifiers: the 80 GPD at ₹650 for a standard pump, the 100 GPD at ₹800 where the pump is rated for it, and the molded high-TDS membrane at ₹900 for feed above 2000 ppm. On hard water a membrane that scaled up in months will do it again; the hard water and appliances guide explains why, and what goes ahead of the purifier to stop it.
The five causes in one table
| Order | Cause | How to confirm | Fix and cost | Who |
|---|---|---|---|---|
| 1 | Sediment cartridge loaded | Brown along its length; ring in the bowl | New cartridge, ₹190 | You |
| 2 | Carbon block blinded or past a year | Still slow after step 1; TDS ratio unchanged | New carbon cartridge, ₹220 | You |
| 3 | Weak inlet supply | Bucket test at the inlet tube | Tap, tube, tank level; usually free | You |
| 4 | Pump worn | Whine or rattle with fresh cartridges and good supply | LUX-PUMP-100, ₹1,299 | Technician |
| 5 | Membrane scaled or worn | Output TDS doubled from day one | 80 GPD ₹650 to molded ₹900 | You, with care |
| — | Cold feed in winter | Slow in the cold months only, TDS steady | Nothing; flow returns as the water warms | Nobody |
Cold water passes through a membrane more slowly, and a purifier in a cold winter can be noticeably slower in January than in June with nothing wrong. If the slowdown arrived with the cold and the TDS ratio is steady, wait for the water to warm before spending anything.
Questions
Why is my RO water flow so slow?
In order of likelihood and cost: a sediment cartridge loaded with silt, a carbon block that is blinded or past its year, weak supply at the inlet, a worn pump, and last a scaled membrane. Check them in that order. A ₹190 sediment cartridge fixes most slow purifiers; the membrane is the answer only when the output TDS has also doubled.
Can a clogged filter make an RO purifier slow?
Yes, and it is the most common cause. The sediment cartridge catches sand, rust and silt, and as it loads it starves the pump of water; the pump whines and the tank crawls. Look at the cartridge: brown across most of its length means it is done. Change it before suspecting the pump or the membrane.
Should I replace the RO membrane if the flow is slow?
Not on slow flow alone. A tired membrane cuts flow and raises output TDS together, so read feed and output with a meter. If the output is still a few percent of the feed, the membrane is fine and a cartridge, the supply or the pump is the cause. Replace it when the reading has roughly doubled from day one and the cartridges are fresh.