- Keep a permanent asset record for the UV unit as well as dated operating and maintenance entries.
- Record the information your actual system provides: lamp status, run time, UV intensity, flow, alarms or shut-off events where available.
- Link lamp and sleeve work to invoices, service sheets, parts used and recommissioning checks.
- Keep UV events alongside upstream filter, turbidity, UVT or source-condition records when they may affect UV performance.
- Do not confuse your operational UV file with the separate statutory records that Regulation 14 requires local authorities to maintain.
Why UV treatment records matter
A UV unit is easy to forget when the controller is quiet and water continues to flow. The problem with relying on memory is that faults and water-quality changes often make sense only when you can look backwards: when was the lamp fitted, when was the sleeve last cleaned, had a pre-filter become dirty, was there a power cut, did intensity fall gradually, and who recommissioned the unit after work?
DWI recommends accurate maintenance records, schematics and plans because they support the private-supply risk-assessment process. Its treatment guidance also says manufacturers’ operating and maintenance instructions should be followed and that maintenance records should be kept. For UV specifically, DWI describes lamp status, run time, intensity monitoring, alarms, automatic shut-off and systematic cleaning or replacement as important parts of operating a UV system.
Create the UV asset baseline
Start with information that changes rarely. This prevents every service visit from beginning with somebody trying to identify the unit or find a missing manual.
- manufacturer, model and serial number where available;
- installation and commissioning date, if known;
- location of the reactor, controller and any automatic shut-off valve;
- where the UV unit sits in the source-to-tap treatment train;
- maximum design flow or other operating limits supplied for the unit;
- lamp type and manufacturer-specified replacement lamp reference;
- quartz sleeve and sensor details where applicable;
- manufacturer’s operation and maintenance instructions;
- installer or service-provider details;
- any commissioning sheet, validation information or design documentation supplied with the unit;
- the upstream treatment that protects the UV stage, such as sediment filtration or iron/manganese treatment;
- the normal controller state and the readings that the operator is expected to check.
Also put the UV unit on the supply schematic. DWI’s record-and-schematic guidance specifically illustrates treatment systems as part of the information useful for risk assessment. A future owner, technician or local-authority officer should be able to see where the UV stage is and what feeds it without reconstructing the system from pipework alone.
Routine operating records: keep what is actually useful
Not every private water supply has the same controller. Some small units show only lamp status and accumulated run time; others show UV intensity, flow, alarms or an automatic shut-off state. Record the information that is meaningful for the installed system rather than inventing a checklist the equipment cannot support.
DWI’s general private-supply maintenance guidance gives daily (or more frequent) checks on the operation of disinfection equipment as an example of proactive maintenance. That should not be turned into a universal statutory “daily UV log” rule. The actual routine should follow the equipment instructions, the risk assessment, the nature of the supply and any local-authority or competent-professional advice.
- date and time of the check;
- operator or responsible person;
- lamp status;
- lamp-hours or remaining-life display where available;
- UV intensity or dose-related display where the unit provides one;
- flow or shut-off status where monitored;
- alarm or warning state;
- visible leaks, damaged fittings or unusual controller behaviour;
- any unexpected colour, turbidity or source condition noted at the same time;
- action taken if the reading is outside the site’s expected operating range.
Consistency matters more than decorative detail. If the same reading is recorded in the same units every time, a falling trend becomes visible. A sequence of unexplained “OK” entries is much less useful than actual readings and observations.
Lamp and sleeve maintenance records
Lamp replacement and quartz-sleeve care belong in the permanent UV history, but this guide is not a replacement procedure. Use the manufacturer’s instructions and, where appropriate, a competent technician. The separate UV lamp replacement guide covers the lamp-change event in more detail.
DWI notes that UV output reduces as lamps age and that a lamp can still look illuminated after useful output has declined. It also explains that scale or fouling on a quartz sleeve reduces transmission. That is why a good record captures more than “lamp changed”.
- date the lamp was fitted or changed;
- lamp run time or controller reading at replacement where available;
- replacement lamp identification or part reference;
- who completed the work;
- sleeve condition and whether it was cleaned or replaced;
- deposit or fouling observed, especially if it is recurring;
- sensor cleaning, inspection or calibration work where applicable;
- seals, O-rings or other parts replaced;
- controller timer reset or service setting changed;
- invoice, service sheet or parts evidence attached to the entry;
- restart, warm-up and normal-status checks after the work.
If sleeve fouling is returning much sooner than expected, link the record to water chemistry and upstream treatment rather than treating every clean as an isolated maintenance job.
Alarms, power failures and automatic shut-off events
A UV event log should preserve the state of the system before somebody clears the alarm. DWI says that where a lamp or power failure occurs and flow is not automatically interrupted, the water produced during the failure is not disinfected by that UV process. It also recommends alarms or failsafes and automatic shut-off features where practicable.
For a fault, capture the evidence needed to understand what happened: exact alarm message, time first seen, controller readings, whether flow stopped, any known power-loss duration, water use during the event, checks carried out, parts or settings changed, and when the unit returned to its normal operating state.
Use the dedicated UV troubleshooting guide for diagnosis. This page’s job is to make sure the incident leaves a usable audit trail rather than disappearing after the reset button is pressed.
Link upstream treatment and water-quality changes
UV performance does not depend on the UV reactor alone. DWI explains that water quality and flow affect UV efficiency. Colour and organic matter can reduce UV transmittance (UVT), suspended material can shield microorganisms, and fouling can reduce the amount of UV reaching the water.
That makes cross-referencing especially useful. If a low-intensity warning coincides with heavy rainfall, visible turbidity, a dirty pre-filter or a recurring iron/manganese problem, record the connection. The separate turbidity guide and pre-filtration guide cover those issues in depth.
- filter cartridge changes, pressure loss or backwash events;
- turbidity results or observations;
- UVT measurements where used by the installed system or service provider;
- iron, manganese, hardness or other water-quality information relevant to fouling;
- heavy rainfall, flooding, source disturbance or seasonal changes;
- pump, plumbing or demand changes that could alter flow through the reactor.
Keep the detailed maintenance in the relevant asset record, then link or reference it from the UV entry. That avoids duplicating the same information across several logs while preserving the relationship between events.
Servicing and recommissioning evidence
A service visit should leave enough information for the next person to understand what was checked and what changed. Keep the contractor’s sheet or invoice, but also record the operational outcome in the supply history.
- date, technician and service company;
- reason for the visit: routine service, alarm, treatment change or repair;
- lamp, sleeve, sensor, ballast/controller or valve work completed;
- readings or test results recorded by the technician;
- parts fitted and any updated maintenance interval;
- faults or defects found but not yet rectified;
- follow-up action, responsible person and due date;
- time the unit was returned to service;
- normal controller/alarm state after restart;
- any advice on flushing, hygiene, sampling or further investigation.
DWI says lamps should be allowed to reach operating temperature before water passes through the unit and that manufacturer instructions should be followed for operation and maintenance. If recommissioning involved more than a straightforward routine task, record who confirmed the system was ready to return to service and on what evidence.
How UV records fit with sampling and the risk assessment
UV operating records, laboratory results and the risk assessment answer different questions. A controller log can show how the UV stage behaved. A sample gives information about water quality at a particular place and time. The risk assessment considers hazards and controls across the whole supply.
Regulation 5(2) requires the relevant person, where disinfection forms part of the preparation or distribution of the water, to maintain and verify the effectiveness of the disinfection process. DWI explains that verification may involve online monitoring, regular sampling or other appropriate means. Your UV record helps preserve that evidence, but the existence of a maintenance log alone does not demonstrate that disinfection was effective.
When a sample is taken because of a UV fault, treatment change or follow-up investigation, link the laboratory report to the event that triggered it. Keep the original report rather than typing only “passed” or “failed”. If the result is unsatisfactory, use the failed private water supply test guide and follow the local authority or laboratory advice relevant to the supply.
How long to keep UV records, and what to hand over
Keep enough history to show the life of the asset and support risk assessment, maintenance, fault investigation and handover. In practice that means retaining old lamp/service dates, significant alarms, changes to the treatment train, commissioning documents and evidence for major repairs rather than deleting everything when a new service year begins.
There is an important legal distinction here. DWI’s Regulation 14 guidance says local authorities must maintain specified records for private water supplies and keep those records for at least 30 years. That is a duty on the local authority; it should not be rewritten as a blanket rule that every owner must keep every UV maintenance entry for 30 years.
When responsibility changes, hand over the manual, unit details, service history, recent operating records, unresolved defects, spare-part information, contractor contacts and any linked risk-assessment or sampling evidence. A new owner or operator should not have to start the treatment history from zero.
Practical UV treatment record template
A simple record can work well if it captures the right facts. The fields below can be adapted to a spreadsheet, paper log, maintenance system or Private Water Supply Manager workspace.
- Asset: supply name, UV unit, model/serial and location.
- Date/time: when the check, maintenance or event occurred.
- Event type: routine check, lamp change, sleeve clean, service, alarm, outage, repair or recommissioning.
- Operating evidence: lamp status, run time, intensity, flow or alarm state where available.
- Incoming-water context: filter status, turbidity/UVT or unusual source conditions where relevant.
- Work completed: what was inspected, cleaned, changed or adjusted.
- Person: operator, technician or contractor responsible.
- Attachments: photographs, service sheets, invoices, controller screenshots or laboratory reports.
- Outcome: normal status, unresolved defect or further action required.
- Follow-up: owner, due date, sampling, professional advice or local-authority action where applicable.
The treatment maintenance planner can help set the next due date, while the wider private water supply record-keeping guide explains how UV evidence fits with the rest of the supply file.
Common UV record-keeping mistakes
- Recording only lamp changes: misses alarms, sleeve fouling, controller readings, outages and upstream conditions.
- Writing “serviced” with no evidence: keep the service sheet and say what work was actually done.
- Resetting an alarm before recording it: capture the code, display and operating state first.
- Keeping UV records separate from filter and water-quality history: this can hide recurring upstream causes.
- Treating a glowing lamp as proof of performance: DWI notes that visible light does not prove sufficient UV output.
- Treating a service certificate as a water-safety certificate: service evidence covers the work performed, not the safety of the whole supply.
- Deleting old records at each lamp change: removes the trend information that makes repeated faults easier to understand.
- Back-filling unknown times or readings: record uncertainty honestly rather than creating false precision.
Frequently asked questions
What records should I keep for a private water supply UV system?
Keep a baseline record for the unit and an operating history. Useful evidence includes the make and model, installation and design information, manufacturer instructions, service contacts, lamp and sleeve maintenance, relevant controller or intensity readings, alarms, power failures, automatic shut-off events, upstream treatment changes, servicing and recommissioning evidence.
Do I need to record UV intensity every day?
Not every private supply has the same UV monitor or operating regime. DWI gives regular checks of disinfection equipment as part of proactive maintenance, but the frequency and readings to record should follow the installed unit, its instructions, the site risk assessment and any local-authority or competent-professional advice. If an intensity reading is available and operationally important, keeping it consistently makes trends much easier to interpret.
Do private water supply owners have to keep UV records for 30 years?
Do not confuse an operator’s UV maintenance file with Regulation 14. DWI explains that Regulation 14 requires local authorities to maintain specified private-supply records and keep those records for at least 30 years. That does not create a blanket 30-year retention rule for every owner’s UV maintenance log. Keep the UV history long enough to support the supply’s risk assessment, maintenance, fault investigation and handover, and follow any specific local-authority or contractual requirement that applies.
What should I record when I replace a UV lamp?
Record the date, lamp identification where useful, lamp-hours or controller reading where available, who carried out the work, sleeve condition and any cleaning, alarms or parts changed, restart and warm-up checks, and the unit’s status after recommissioning. Keep invoices or service sheets with the asset record rather than relying on a diary entry alone.
What should I record after a UV alarm or power failure?
Capture the time, alarm message or code, whether water flow stopped automatically, how long the failure may have lasted, any water that could have passed during the event, checks and repairs completed, restart or recommissioning details and any professional, laboratory or local-authority advice. The separate UV troubleshooting guide covers fault diagnosis in more detail.
Does a UV service certificate prove the private water supply is safe?
No. A service certificate is useful evidence of work carried out on the UV asset, but it is not proof that the whole supply is safe or compliant. UV effectiveness also depends on water quality, flow, sleeve condition, the treatment train and operation within the unit’s design criteria, while water-safety decisions may require sampling, risk-assessment information and site-specific advice.
Should I keep upstream filter and water-quality records with the UV record?
Yes, where they affect UV performance. DWI explains that water quality and flow influence UV efficiency and that suspended matter, colour and organic matter can reduce performance or contribute to fouling. Linking filter changes, turbidity or UVT information, rainfall or source changes and UV alarms can reveal patterns that are invisible when each record is kept separately.
Keep the UV asset, maintenance, faults and follow-up connected.
Private Water Supply Manager can keep treatment assets, maintenance dates, documents, corrective actions and sampling evidence in one supply-specific record trail.
- DWI: Record keeping
- DWI: UV disinfection
- DWI: Examples of records and schematics
- DWI: Information note on Regulation 5
- DWI: Information note on Regulation 14
Regulatory and technical guidance can change. Check current DWI material, the manufacturer’s instructions and your local authority or competent adviser for the position applying to your supply.