- For applicable supplies, Regulation 6 places the statutory risk-assessment duty on the local authority; competent contractors may act on its behalf.
- Applicable assessments must be reviewed at least every five years, and sooner where the authority considers the assessment inadequate or circumstances have changed significantly.
- A single dwelling with no commercial or public activity is normally exempt unless the owner or occupier requests an assessment.
- DWI treats risk assessment as a proactive source-to-tap process: sampling is important evidence, but it is not a substitute for assessing hazards and controls.
Why risk assessment matters
A private water supply can produce a satisfactory laboratory result on one day and still contain weaknesses that could cause contamination later. That is why the regulatory approach looks at hazards and controls throughout the lifetime of the supply.
The practical value of the assessment is highest when it reflects how the system actually works. An old diagram, missing treatment records or uncertain responsibilities can hide risk and make corrective actions harder to prioritise.
Which supplies need a Regulation 6 risk assessment?
In England, the local authority must risk assess applicable private water supplies in its area. DWI identifies the principal exception as water supplied only to a single dwelling where there is no commercial or public activity. In that case a statutory risk assessment is not normally required unless the owner or occupier asks the local authority to carry one out.
Shared supplies, Regulation 8 private distribution systems and Regulation 9 commercial or public supplies fall within the risk-assessment regime. A single dwelling used for a commercial or public activity is not protected by the single-dwelling exception.
Map the supply from source to tap
- Identify every source: spring, borehole, well, surface-water intake or incoming mains connection.
- Show collection chambers, pumps, raw-water tanks, filters, dosing equipment, UV units, treated-water tanks and branch lines.
- Mark drinking-water points, public or commercial users, rarely used outlets and any cross-connections.
- Record where samples are normally taken and where treatment performance can be checked.
A schematic does not need to be artistic. It needs to be current, legible and tied to real assets on site. If an assessor or contractor refers to “UV 2” or “Tank B”, those labels should mean the same thing in the diagram, maintenance record and evidence folder.
Source and catchment hazards
The source is the first barrier. Consider land use, livestock, septic tanks, drainage, flooding, runoff, access, vandalism, wildlife, damaged covers and changes following heavy rainfall. Groundwater and spring sources can behave differently from surface water, and shallow sources may respond quickly to weather.
Keep dated photographs and notes when source conditions change. Evidence of a repaired spring chamber, improved fencing or drainage work can be as important operationally as a laboratory result because it shows that a hazard was recognised and controlled.
Treatment controls
Treatment should be appropriate to the actual raw-water quality and hazards. A system may include several barriers — for example sediment removal, specialist media and disinfection — and each stage needs its own operating and maintenance evidence.
For UV, record lamp changes, sleeve cleaning, alarms, power failures and maximum-flow controls. For filters, record cartridge or media changes and pressure/flow observations. For chemical dosing, retain product information, settings and service records. Never treat “the plant was serviced” as sufficient detail if several assets were involved.
Storage and distribution
Tanks, lids, vents, overflows, access hatches, dead legs and long distribution networks can introduce or amplify risk after treatment. Record inspections, cleaning, repairs and any suspected ingress.
Where multiple properties or businesses share the same source, responsibilities should be clear. Who checks the source? Who services treatment? Who receives laboratory reports? Who can authorise emergency work? Operational ambiguity is itself a management weakness.
Sampling evidence
Sampling supports the risk picture but does not replace it. Keep sample location, reason, date, sampler, laboratory report and follow-up together. Trend results where useful, especially when a parameter changes after rainfall, maintenance or treatment adjustment.
If a result is unusual, do not simply file the PDF. Record who reviewed it, what advice was received, what action was taken and what evidence closed the action.
After the assessment
Convert recommendations into named actions with an owner, due date and evidence requirement. Some actions may be urgent; others may be planned improvements. The important point is to avoid a risk-assessment report becoming a static document that is rediscovered years later.
Keep the complete original assessment, not only a summary. Link each action back to the relevant supply component so future reviewers can understand the history.
When to review before five years
Five years is the outer review cycle for applicable assessments, not a reason to ignore change. DWI says a local authority should review an assessment whenever it considers the current assessment inadequate or circumstances have changed significantly.
Examples include deterioration in raw-water quality, a new or reinstated source, significant treatment changes, altered storage or distribution, a new commercial/public use, extension to additional premises or recurring water-quality problems. Record the change promptly and contact the local authority so it can decide whether the statutory assessment and monitoring plan need revision.
Practical checklist
- Current supply schematic with labelled assets.
- Source and catchment description with access arrangements.
- Treatment specifications, manuals and service history.
- Tank and distribution inspection records.
- Latest laboratory reports and sampling locations.
- Incident and complaint history.
- Open and closed corrective actions.
- Evidence of significant changes since the last assessment.
A source-to-tap risk assessment walkthrough
1. Source and catchment
Start by understanding how water can become contaminated before it reaches any treatment. For a spring this may mean surface runoff, damaged collection chambers, livestock access or changes after heavy rain. For a borehole it can include headworks condition, nearby drainage, land use and the integrity of the abstraction. For a surface source the variability can be greater and treatment may need to cope with rapid changes in turbidity and microbiological load.
Operational records should include source photographs, access arrangements, catchment observations and important weather or land-use events. These records do not replace assessment, but they make recurring patterns visible.
2. Abstraction, pumping and raw-water storage
Pumps and tanks affect flow, retention and the hydraulic conditions seen by treatment. A replacement pump with a higher flow rate can inadvertently push water through filters or UV faster than the original design. Raw-water tanks can accumulate sediment or allow ingress if covers, vents and overflows are not protected.
3. Treatment barriers
Each treatment stage should have a defined purpose. A sediment cartridge may protect a UV unit; an iron-removal vessel may prevent staining and downstream fouling; a UV reactor may provide final disinfection. If nobody can explain what a vessel is for, how it is maintained or what indicates failure, that is an operational weakness worth resolving.
4. Treated-water storage and distribution
Risk does not stop at the treatment-room door. Treated storage, long pipe runs, rarely used outlets, poor tank hygiene and cross-connections can affect water after disinfection. Map every significant component to the consumer tap.
How to prepare for the assessor’s visit
Before the visit, create a simple evidence index rather than handing over an unsorted folder. Put the current schematic first, then the previous assessment, sampling history, treatment details, maintenance, incidents and open actions. Label assets consistently so documents can be matched to physical equipment.
Walk the site yourself using the schematic. If a pipe route, tank or treatment vessel on the drawing no longer exists, correct the record before the assessment. Note access constraints and arrange keys, ladders or contractor attendance safely where needed.
Scoring is not the end of risk management
Risk tools often produce scores or categories, but the useful output is the list of hazards, controls and actions. Operators should avoid focusing on a single headline score while ignoring one high-consequence weakness. A damaged source cover, recurring UV alarm or uncontrolled bypass deserves attention because of what can happen, not because of how a spreadsheet total looks.
After the assessment, convert every recommendation into an action with a responsible person and evidence requirement. Then review progress routinely instead of waiting for the next five-year cycle.
Risk assessment for portfolios and shared systems
Consultants, estates and shared supplies need an additional layer of clarity: which hazards are common to the source and which are specific to a property branch? A shared spring may feed several treatment systems, or one treatment plant may feed several buildings. The database and schematic should represent that relationship so a source issue can be traced to every affected consumer.
For portfolios, standard templates are useful only if they allow site-specific hazards. Repeating identical wording across ten supplies can create the appearance of consistency while hiding important differences in catchment, treatment, occupancy or distribution.
Frequently asked questions
How often is a private water supply risk assessment reviewed?
Applicable risk assessments must be carried out and reviewed at least every five years. DWI also says the local authority should review sooner where it considers the assessment inadequate or circumstances have changed significantly.
Can I carry out the statutory risk assessment myself?
The statutory duty remains with the local authority. It may commission an appropriately trained, accredited and competent external person or organisation to carry out the assessment on its behalf, but the authority remains responsible for the assessment and for regulatory decisions arising from it.
What is the most useful document to prepare?
A current source-to-tap schematic is one of the most useful preparation records because it connects the source, treatment, storage, distribution, sampling points and assets to the real system. It supports the assessment; it does not replace it.
Should laboratory reports be part of the assessment evidence?
Yes. They are important evidence, but DWI is clear that sampling alone does not provide the whole assurance picture.
Does every single dwelling need a statutory risk assessment?
No. In England, a supply serving only one dwelling with no commercial or public activity is normally exempt from the Regulation 6 risk-assessment requirement unless the owner or occupier asks the local authority to carry one out. Different rules apply where the water is used for commercial or public activity or the supply serves more than one property.
Keep the records behind this work together.
Use the free tools or start a 7-day trial to see how sampling, maintenance, actions and documents can sit in one source-to-tap record.
- DWI: Regulation 6 risk assessment
- DWI: Risk assessment tools and tips
- DWI: What sampling is required?
- DWI: Private water supply treatment guide
- DWI case study: private supplies require active management
- DWI: Types of private supplies in England
Regulatory guidance can change. Check the current DWI material and your local authority for the position applying to your supply.