RO, UV or UF: which purifier does a Nellore home actually need?

Start with one number: the TDS of the water coming into your house. If it is below about 300 and the supply is treated municipal water, you do not need an RO — a UV plus UF unit protects you from microbes without throwing away three litres for every one you drink. If it is a borewell reading 500, 800 or 1,500, you need an RO, and in Nellore you probably want a UV stage after it. If you are on tankers, you need RO plus UV because you do not know what arrives next week. Everything below is the reasoning behind those three sentences.

What each technology does — and does not do

• RO (reverse osmosis). Forces water through a membrane that holds back dissolved salts, hardness, fluoride, nitrates and most heavy metals. It is the only one of the three that lowers TDS. Needs a pump and power, produces reject water, and strips taste-giving minerals along with the unwanted ones.
• UV (ultraviolet). A lamp that inactivates bacteria and viruses as water passes. Removes nothing physical — no salts, no turbidity, no smell. Needs power, and needs clear water to work, so it always sits after a sediment or UF stage.
• UF (ultrafiltration). Hollow fibres fine enough to stop bacteria, cysts and silt but not dissolved salts. Works without power on tap pressure. Ideal where TDS is already low and the worry is contamination, not hardness.

Most units sold here are combinations: RO+UV, RO+UV+UF, UV+UF. The right combination follows the water.

Match the purifier to the source

Municipal or canal supply (treated, chlorinated). TDS is typically low to moderate. Chlorine handles microbes at the treatment plant, but the pipe between the plant and your tap is not always clean, especially after the monsoon when road-side lines sit in standing water. A UV+UF with a carbon pre-filter (for the chlorine taste) is the sensible choice. An RO here is not harmful; it is just wasteful and makes flat-tasting water unless it has a mineraliser.

Borewell. This is most of Nellore outside the piped zones, and most borewells are hard and high in TDS. Iron and salt are common, and the eastern coastal belt — Muthukur, Krishnapatnam, villages towards the sea — can show brackish readings that rise in summer. RO is the only thing that brings that down. Add UV after the RO: bores near septic tanks or open drains can carry bacteria, and the RO storage tank itself can grow a film over time.

Tanker water. Unknown source, unknown TDS, unknown handling. Treat it as the hardest case — RO+UV — and measure the output now and then. If you are on tankers only in summer, the same unit handles municipal water the rest of the year; just let the technician set the TDS controller so the output does not taste dead on the cleaner supply.

Mixed or sump water. Many homes pump borewell and municipal water into the same sump. The purifier sees a blend that changes with the season. Measure the sump, not the bore or the tap, and buy for the higher end of what you see.

Reading the TDS number sensibly

A handheld meter gives a number in parts per million. As a rough guide: under 300 tastes good to most people and needs no RO; 300 to 500 is borderline and comes down to taste and hardness; above 500 is where the BIS drinking-water standard's acceptable limit sits and an RO starts to make sense; above 1,000 an RO is needed, and the membrane will work hard.

TDS tells you about dissolved salts, not about bacteria. Low-TDS water can still be unsafe, which is why UV or UF belongs in every unit regardless of the number.

Things to check before buying

• Inlet pressure. RO pumps are built for normal mains or overhead-tank pressure. A direct line from a motor can be too much for push-fit joints; a very low gravity feed may not give enough.
• Reject water. An RO will produce roughly two to three litres of reject for every litre purified. Plan where it goes — a bucket, a drum, the drain.
• Power. Evening voltage dips in summer are hard on the small SMPS adapter that runs the pump and UV lamp. A stable socket, not a loose board shared with the mixer, helps.
• Storage. Long power cuts favour a unit with a decent tank or a UF fallback.
• Service access. Filters come out from the front or the side; a unit squeezed into a corner above the sink is a pain to service.

When to call a technician rather than guess

If you do not own a TDS meter, a technician can measure the inlet, tell you the hardness and sediment load, and recommend a configuration for your actual water rather than the one on the billboard. If you already own a purifier and the water tastes wrong, that is a service question, not a replacement question: a multi-stage flush on our rate card is ₹299, and it will tell you whether the unit is the right type for your supply.