An annual service contract treats every house the same. Your water does not. Here is what each stage of an RO actually does, and how groundwater in Rohtas and Kaimur decides the real schedule.
Most people know their purifier has "filters" and that someone comes once a year to change them. Very few know what the stages are for, which is why it is hard to tell a genuine service from an unnecessary one.
It is worth understanding, because the right service interval for a house in Mohania drawing hard, iron-heavy groundwater is not the same as for a house on a cleaner municipal supply. One calendar does not fit both.
What each stage actually does
The sediment filter
This is the first stage and it is simply a mechanical strainer. It catches sand, silt, rust particles and visible turbidity. It is a sacrificial part — it is meant to clog, because everything it holds is something the delicate stages downstream never have to deal with.
In our area this is the stage that fills fastest, particularly where the supply comes from a borewell or where the overhead tank stirs up sediment. During monsoon, when water anywhere near surface sources runs dirty, it fills faster still.
The pre-carbon filter
Activated carbon. It takes out chlorine, some organic matter, and a lot of what makes water taste and smell unpleasant. Its other job is protective: chlorine damages the RO membrane, so the pre-carbon stage is effectively the membrane's bodyguard. A neglected pre-carbon filter shortens membrane life.
The RO membrane
This is the expensive part and the heart of the machine. It is a very fine semi-permeable membrane, pushed by a pump, that separates dissolved salts, hardness, heavy metals and most contaminants from the water. What passes through goes to your tap; what does not goes down the reject line.
A membrane is not a filter you rinse. It either works or it is losing performance, and with hard or iron-heavy feed water it works harder and its life is shorter.
The post-carbon filter
A polishing stage. It sits after the membrane and tidies up the taste and odour of the finished water before it reaches the tap.
UV, UF and mineral stages
Not every machine has all of these. A UV lamp inactivates bacteria and viruses, and its output falls over time even while the lamp still glows — which is why UV lamps are replaced on schedule rather than when they stop lighting. A UF membrane is a coarser physical barrier that works without electricity. A mineral cartridge adds back some of what the RO removed, because RO water on its own tastes flat.
So how often should stages be changed
Honestly: it depends on your water and your usage, and any answer given without knowing either is a guess dressed up as a schedule.
- Sediment — the most frequent by a distance. Where water is silty or iron-heavy, it needs changing several times a year, and a house on clean supply can go much longer.
- Pre-carbon — regularly, and never stretched, because the membrane is what pays for that delay.
- Membrane — measured in years, not months, but shortened sharply by hard water, by running without a working pre-filter, and by long idle periods.
- Post-carbon — periodically, generally when taste starts to flatten.
- UV lamp — on schedule, because output drops long before the lamp dies.
The practical approach is to have the input and output water checked on each visit and change what has actually gone, rather than replacing the whole set because twelve months have passed. If a technician wants to change every cartridge on every visit without checking anything, ask why.
Insist on this: ask the technician to show you the input and output reading before and after the work, and ask for the old cartridge to be left with you. A membrane is the most expensive part in the machine and also the easiest one to charge for without fitting. A bill listing exactly what was fitted protects you.
Our groundwater, and why it matters here
Across much of Rohtas and Kaimur the groundwater is hard, and in many pockets it carries iron. Households in and around Sasaram, Bhabhua, Mohania and Kudra will recognise the signs: a yellowish or reddish tinge when a tap runs after standing, orange-brown staining in the washbasin and on white clothes, a metallic taste, and white crust on taps and utensils.
Iron is particularly hard on an RO, because dissolved iron oxidises on contact with air and deposits as fine rust inside the pre-filters and on the membrane surface. It fouls the membrane from the outside in. In houses like that, an RO installed with no iron-removal or pre-treatment stage ahead of it will get through membranes faster, and the owner will be told repeatedly that the membrane "has gone" without anyone addressing the reason.
If your supply is visibly iron-heavy, the right conversation is about pre-treatment, not about buying a bigger purifier.
Signs the membrane is failing
- The output water starts tasting salty, flat or "like the tap again" — the clearest sign, because it means dissolved solids are passing through.
- The purified output slows to a trickle while the reject line still runs normally.
- The tank takes much longer to fill than it used to.
- The machine runs almost continuously and cuts off late or not at all.
- Water quality falls away shortly after a service in which the membrane was not changed.
Some of these can equally be a tired pump, a faulty float or solenoid valve, or a choked pre-filter starving the pump. That is exactly why a reading before and after matters. A membrane should be changed because a test says so, not because a year has gone by.
Water wastage, and what to do with it
Every RO rejects water. That is how it works — the reject stream carries away what the membrane has separated, and a machine that rejects nothing is a machine whose membrane is bypassed or finished. The proportion varies with the machine, the feed water and the pressure, and it rises as the membrane ages or the pre-filters clog.
What you can control is where that water goes. Run the reject line into a bucket or a drum and use it for mopping, flushing, washing the courtyard or the scooter. Do not use it for drinking, for cooking or for a pet, and do not put it on plants you are careful about, because it carries concentrated salts. A neat length of pipe to a storage drum takes ten minutes to fit and is the single most useful change most households can make.
Other things that go wrong
Not every purifier complaint is a filter. A machine that will not start at all usually points to the adaptor, the pump or the low-pressure switch. Constant running and overflowing is usually the float valve or the auto cut-off. Leaks are normally a tube that has worked loose at an elbow, or a housing cracked by overtightening. A loud knocking pump often means it is running dry because the inlet is closed or the pre-filter is solid.
And one that matters after a holiday: if a purifier has stood unused for weeks, do not drink the first tank. Run it off and let it refill.
Getting it serviced
We service and repair RO and UV water purifiers, change individual stages rather than whole sets when that is what is needed, and fit pre-treatment where the feed water calls for it. Current charges are on the rate list, with GST extra. Cartridges, membranes and lamps are billed at actual cost after we tell you what is needed and why, and you get a bill listing every part fitted.
Booking online gets you a callback within an hour, or call +91 96315 11974 between 8:00 AM and 6:30 PM on any day.
We cover water purifier service in Sasaram, Bhabhua, Mohania, Kudra, Nokha and beyond — the full list is on the service areas page.
Frequently asked questions
There is no single answer, because it depends on your water and how much you use. The sediment filter goes first and fastest, especially with borewell or iron-heavy supply. Pre-carbon follows and should never be stretched, since it protects the membrane. The honest approach is to have the water checked each visit and change only what has gone.
The clearest sign is taste — the water starts tasting salty, flat or like ordinary tap water again, which means dissolved solids are getting through. Purified output slowing while the reject line runs normally, and a tank that takes far longer to fill, point the same way. Ask for an input and output reading before agreeing to a replacement.
Yes, and you should. Run the reject line into a bucket or drum and use it for mopping floors, flushing, washing the courtyard or cleaning a vehicle. Do not drink it, cook with it, give it to animals, or use it on plants you care about, because it carries the concentrated salts the membrane removed.
Usually one of three things. The post-carbon polishing stage was not changed, so taste and odour are not being finished off. The membrane is passing dissolved solids and was not actually replaced. Or water has been sitting in the tank and tubing unused. Empty the tank, let it refill, and if the taste persists ask for a reading.
Want a hand with this?
Book a technician at home across Sasaram, Rohtas, Kaimur and Aurangabad. Prices fixed up front, a bill for every job.