RO Service Checklist: What a Technician Should Check During Every Visit
A proper RO service visit is more than a filter swap. Here is what a complete inspection should include.
Step 1: Complete visual inspection of the purifier
A proper service starts before any tools come out. The technician should inspect: the outer cabinet and mounting bracket for damage or instability; all visible tubing and push-fit connectors for drips, staining, or signs of slow leaks; the dispensing tap for calcium deposits or mould; the drip tray for standing water (indicates a leak that developed since last service); the storage tank for any signs of exterior corrosion or damage; and any LED or display indicators for active alerts.
Visual inspection catches many issues that are invisible from outside — a slow drip from a push-fit connector typically leaves a white calcium ring visible on the cabinet wall or under-sink cabinet floor. Discolouration of tubing can indicate bacterial growth. These observations should be documented and discussed with you before the service begins, not discovered midway.
Step 2: TDS measurement of both inlet and output water
Before replacing anything, the technician should use a calibrated TDS meter to measure: (a) your tap inlet water TDS — establishing the source water quality; (b) the current purifier output TDS — establishing the pre-service baseline. This two-point measurement determines the membrane's current rejection ratio: (outlet ÷ inlet) × 100. A healthy ratio is below 15–20%. Above 25–30% indicates declining membrane performance.
The technician should record both readings on your service invoice along with the date. This creates a performance baseline for your purifier's history — comparison over multiple service visits reveals whether output TDS is gradually trending upward (early membrane aging) or suddenly jumped (component failure). If a technician does not test both inlet and outlet TDS before starting work, ask them to do so. It takes 2 minutes and provides the most important diagnostic information available.
Step 3: Water flow rate assessment
The technician should assess how quickly purified water fills a glass or one-litre container from the purifier tap. Standard domestic RO purifiers should fill a glass in 20–40 seconds and produce approximately 8–15 litres per hour depending on model and feed pressure. Slow flow (taking more than 60 seconds for a glass) indicates one of: clogged sediment or carbon pre-filter; low inlet water pressure (below 5–10 psi for most models); membrane scaling or fouling; booster pump degradation; or a low-pressure storage tank.
Slow flow is often blamed on the membrane but is far more frequently caused by clogged pre-filters or low pressure. The technician should check filter condition first. If replacing pre-filters restores normal flow, a membrane replacement was not needed. If flow remains slow after filter replacement and pressure is confirmed adequate, membrane condition becomes the next investigation point.
Step 4: Filter condition inspection and replacement with documentation
The technician should remove each pre-filter and post-filter stage, inspect the cartridge visually (a heavily brown, compressed, or foul-smelling cartridge is well beyond service life), clean the filter housing and O-rings, and install fresh replacements. For Hyderabad homes on borewell or tanker water, pre-filters may look surprisingly clogged even after only 4–5 months — this is normal for high-sediment sources.
Insist that replaced filters are shown to you before disposal — a heavily clogged cartridge removed from your purifier is evidence that the service was due. A technician who replaces filters but does not show you the used ones is harder to trust. Also request that the brand name and specification of replacement filters be noted on the invoice — this allows you to verify quality and compare against future replacements.
Step 5: Membrane performance evaluation before assuming replacement
Membrane performance should be assessed from the TDS rejection ratio measured in Step 2 — not from flow alone. A membrane with 85% rejection (inlet 500 ppm, outlet 75 ppm) is performing well. A membrane with 70% rejection (inlet 500 ppm, outlet 150 ppm) is declining. Below 65% rejection (inlet 500 ppm, outlet 175+ ppm) signals membrane failure needing replacement.
A crucial best practice: pre-filters should be replaced first (Step 4) and then output TDS re-tested before deciding on membrane replacement. Clogged pre-filters reduce pressure at the membrane, causing artificially elevated outlet TDS. After fresh pre-filters are installed and the system runs for 15–20 minutes, measure TDS again. If rejection improves significantly, the membrane was not at fault — the pre-filters were. This single step saves many unnecessary membrane replacements.
Step 6: Drain water and shut-off valve check
When the storage tank is full, the automatic shut-off valve (ASOV) should stop the purification cycle and the drain line should have no water flow. If water continues draining when the tank is full, the ASOV has failed and should be replaced. A continuously draining purifier wastes significant water — at a typical drain rate, a stuck ASOV can waste 50–100+ litres per day.
The technician should also verify the drain water flow rate during purification is appropriate for the membrane size — a 75 GPD membrane in a standard 1:3 or 1:4 ratio system should produce roughly 3–4 litres of drain water per litre of purified water. Significantly higher drain ratios suggest membrane fouling is causing poor efficiency.
Step 7: Service documentation and clear handover
Before leaving, the technician should provide a written service record (physical receipt or WhatsApp photo of the invoice) that documents: service date; purifier model and serial number; all parts replaced with brand specifications; pre-service TDS readings (inlet and outlet); post-service TDS readings (inlet and outlet after fresh filters and any replacements); any observations or recommendations; and the recommended next service date.
A service record with both pre- and post-service TDS readings is the single most valuable piece of documentation you can have for your purifier. It proves the service was performed, confirms the parts were replaced, and establishes the baseline for the next visit. Insist on it every time. If the technician does not offer it, ask before they leave.
Frequently Asked Questions
How long should a complete RO service visit take?
A thorough preventive service visit with filter replacement, TDS testing, and housing cleaning should take 40–60 minutes. A quick 15-minute filter swap without TDS testing, flow assessment, and proper documentation is not a complete service.
Should I be present during the RO service visit?
Yes. Being present allows you to ask about any issues found, see the used filters being removed, confirm the parts being installed, and receive the service record directly. Unsupervised service visits give you less visibility into what was and was not done.
What if the technician insists on replacing the membrane during a routine visit?
Ask them to show you the TDS readings (inlet and outlet) and the calculated rejection ratio. If rejection is above 80%, the membrane is typically fine. If they cannot provide current TDS readings or insist on replacement based on flow alone without testing, that is a red flag — request a second opinion.
