How often do RO filters really need changing in Nellore? Go by TDS

The honest answer is: it depends on the water going in, and in Nellore that varies street by street. A family on treated municipal supply can go a year between filter changes. A family two lanes away on a borewell with a TDS of 1,200 and fine silt in the sump can choke a sediment filter in three months and wear a membrane out in under two years. The sticker on the side of the purifier does not know which house it is in. A TDS meter and your own eyes do.

The three things that wear out at different speeds

A typical RO purifier has four or five stages, and they do not age together.

• Sediment filter (the white candle). Catches silt, rust and sand. It clogs by volume of dirt, so its life is about turbidity. When it turns brown or grey and flow drops, it is done, whether that is month three or month twelve.
• Pre-carbon and post-carbon. Remove chlorine, smell and taste. Carbon exhausts with use and with chlorine load. Municipal water, which is chlorinated, uses it up faster than borewell water. A flat or slightly off taste in otherwise clear water is usually carbon.
• RO membrane. Removes dissolved salts — the TDS. It ages with the amount of salt it has to hold back and with scaling from hardness. High-TDS borewell water is hard on it; low-TDS canal water is gentle. It also dies early if the pre-filters were left to clog, because it then runs starved of flow and pressure.
• UV lamp and UF (if fitted). The UV lamp loses output over roughly a year even while it still glows, so it is replaced on time, not on symptoms. A UF cartridge clogs like a sediment filter and is flushed or replaced.

A realistic Nellore schedule

Water source	Sediment + carbon	Membrane	UV lamp
Municipal / canal supply, TDS under 300	9–12 months	2–3 years	yearly
Borewell, TDS 300–800, some hardness	6 months	18–24 months	yearly
Borewell, TDS above 800, or silty	3–4 months	12–18 months	yearly
Tanker water, source unknown	check monthly; change on colour or flow	measure each service	yearly

These are starting points. The real test is what the filters look like when they come out and what the TDS meter says.

Measure instead of guessing

A handheld TDS meter costs very little and is the single most useful tool for an RO owner. Use it this way:

1. Measure the raw water at the inlet tap once. Write it down.
2. Measure the purified water once a month. Write it down.
3. Watch the trend. Purified water from a healthy RO is usually a small fraction of the input. If the output climbs steadily month on month and is heading past a tenth of the input, the membrane is tiring or the pre-filters are starving it.

Two other signals worth tracking: how long the tank takes to fill from empty, and the colour of the sediment candle if the housing is clear. A fill that took forty minutes last year and takes two hours now is a flow problem, and flow problems are almost always filters or pump.

Why Nellore wears filters faster

• Borewell water in many localities carries high TDS and hardness. The membrane is holding back more salt every litre, and calcium scale builds on it faster. A deeper summer borewell (March to June, when the table drops) often reads higher TDS than the same bore in December.
• Silt after rain. The north-east monsoon stirs up sumps, open wells and bore casings. Sediment filters that were fine in September go brown in November.
• Tanker water. When the supply switches to tankers in summer, the source changes load to load. Treat each tanker as unknown water: check the sediment filter more often and measure the output.
• Intermittent supply. Air in the line from an empty overhead tank makes the pump run dry and the sediment filter see surges of rust from old pipes.

What a filter change visit should include

Not just swapping candles. A proper filter change in Nellore is a service: sediment and carbon replaced as needed, membrane flushed and its output TDS checked, storage tank drained and cleaned, fittings checked for weeping, pump pressure checked, and a TDS reading of the finished water shown to you. On our rate card that visit is ₹299 — filter check and service — with any filter or membrane that actually needs replacing charged at MRP and shown to you before it goes in. If the technician changes everything every visit regardless of condition, ask why.

When to stop waiting for the schedule

Any one of these means book the service now, whatever the date:

• Output TDS has climbed noticeably over two or three monthly readings.
• Flow has dropped to a trickle or the tank takes far longer to fill.
• A taste or smell has appeared in water that used to be clean.
• The sediment candle is visibly brown or slimy.
• Reject water is running constantly even with the tank full.

A filter changed a month early costs a little. A membrane run a year too long on starved flow costs a membrane.