If your site draws water from a borehole, well or spring rather than the mains, you carry two separate duties, not one. The Private Water Supplies (England) Regulations 2016, and their devolved equivalents, govern whether your water is safe to drink. Legionella control is a different obligation entirely, and it applies to you exactly as it applies to a mains-fed building.

That second point is the one people miss. Being off-mains does not exempt you from controlling Legionella risk; the duty under the Health and Safety at Work Act and ACoP L8 follows the system, not the source [1][3].

So you have a drinking-water regime, usually overseen by your local authority, and a Legionella regime you manage yourself through a risk assessment. Getting the boundary clear is what stops you either over-spending on the wrong tests or quietly leaving a real risk unmanaged.

The 2016 Regulations are England, not the whole UK

The title of this article names the 2016 Regulations because that is the English private-water regime. Wales uses the Private Water Supplies (Wales) Regulations 2017; Scotland has its own private-water supply regime through local councils and the Drinking Water Quality Regulator; Northern Ireland uses the Private Water Supplies Regulations (Northern Ireland) 2017 through DAERA / DWI NI [20][21][22][23].

That does not change the Legionella principle. In every nation, the private-water rules are mainly about drinking-water quality and source-to-tap risk assessment. Legionella risk inside the building is controlled through the water-system risk assessment, especially where water is stored, heated, stagnates or is aerosolised. What changes across the UK is the name of the private-water regulation, the regulator and the local reporting route.

For a multi-nation estate, write the source regime into the site record. Do not use the English 2016 shorthand on a Welsh, Scottish or Northern Irish file unless the actual local regulation is named elsewhere.

The core principle: source quality and Legionella control are different questions

The 2016 Regulations are about potability, chemistry, microbiology, whether the water meets drinking-water standards at the tap. Local authorities risk-assess and sample certain private supplies on a schedule set by who and how many people the supply serves. That is a job done largely to you and your supply.

Legionella is about what happens to water after abstraction, once it is sitting in your storage and warming up through your pipework. Legionella pneumophila is a freshwater organism that lives harmlessly at low numbers in groundwater and surface water [13]. It becomes a hazard when your tanks, calorifiers and dead legs give it warmth, stagnation and time to multiply, then an outlet aerosolises it [6].

In my view the cleanest way to hold both in your head is this: the local authority cares whether the water is fit to swallow; your Legionella risk assessment cares whether it is dangerous to breathe in as a spray. A borehole can pass its drinking-water sampling and still feed a hot water system that grows Legionella beautifully. For more on why a natural source stays low-risk until your building amplifies it, see Where Legionella grows: natural and man-made water systems.

Applied across four off-mains situations

A holiday let on a borehole. This is the classic high-risk combination: a private supply, intermittent occupancy, and showers that sit unused between bookings. The Legionella duty here sits with whoever is responsible for the property, typically the owner or managing agent, and it is the same duty a landlord carries on a mains supply [7]. The borehole does not change the assessment much; the void periods do. Stagnant warm water in the cylinder over a quiet fortnight is your real exposure, not the aquifer.

Farm cottages sharing a single supply. Where one borehole feeds several dwellings, the 2016 Regulations may trigger local-authority risk assessment and sampling because the supply serves multiple premises. That tells you about drinking-water quality. It tells you nothing about the Legionella risk inside each cottage’s own hot and cold system, which still needs its own assessment per property.

A rural workplace, workshop, kennels, glamping reception. Here you are an employer or person in control of premises, so the Legionella duty is unambiguous [3]. A simple, low-occupancy site with only cold taps and a small water heater is genuinely low-risk. The pragmatic call is to right-size the effort: document that low risk honestly rather than pretend the duty does not exist.

Reopening after a seasonal close. Off-mains rural sites are often seasonal, and the reopening flush matters more than almost anything else you do. Long shutdowns let temperatures drift into the growth band and let numbers climb undisturbed. Seasonal buildings: managing intermittently used properties covers the recommissioning routine in detail, and it applies squarely to borehole-fed lets and campsites.

Where a private supply genuinely changes your Legionella controls

Mostly the controls are identical to any building: keep cold water stored and distributed below 20°C, keep hot water hot, commonly stored at around 60°C, and keep water moving so nothing stagnates [6]. Treat those as general expectations that your own risk assessment confirms or adjusts; do not lift the figures as fixed law [1].

What the source changes is the upstream picture. Borehole and well water can carry more sediment, iron and manganese, and a richer microbial load than treated mains water. That sediment feeds biofilm, and biofilm shelters Legionella from heat and disinfectant [13]. So storage tank condition and cleanliness carry more weight on a private supply than they might in town.

Two consequences follow. Any disinfection on your supply, UV, chlorination, a treatment unit, is there for drinking-water safety and must not be assumed to control Legionella in your hot system. And cold-water storage discipline matters more, because incoming water may already be warmer and dirtier than mains; keeping that tank cool, covered and clean does double duty. Cold water storage tanks: keeping temperatures low is the companion read.

Field checklist: a borehole or well site walk-round

Use this on a physical walk of the site. Each item is recordable, note the result and the date.

  • Locate and log the source. Borehole, well or spring; record the abstraction point and any treatment unit (UV, filtration, dosing).
  • Confirm the private-water regulations status. Establish whether the supply is regulated in England, Wales, Scotland or Northern Ireland, who risk-assesses or samples it, and where the latest result is held.
  • Inspect cold-water storage. Lid fitted and tight, insect-proof, no light ingress, no visible sediment or scale. Record stored temperature.
  • Check cold distribution temperature. Confirm cold reaches outlets below the growth band as your assessment specifies [6].
  • Check hot generation and storage. Calorifier or cylinder reaching and holding its target temperature; record the figure your assessment sets [1].
  • Walk the pipework for dead legs. Capped spurs, removed appliances, rarely-used outlets, list them for flushing or removal.
  • List little-used outlets. Especially in seasonal lets: outbuilding taps, spare showers, outside hoses near the building.
  • Record the void/flush regime. How outlets are flushed between occupancies or after shutdowns, and by whom.
  • Name the responsible person. Who holds the Legionella risk assessment and acts on it, and the review date.

Record all of this somewhere you can produce on demand. A bound paper logbook works; a digital logbook works better on a remote rural site, because temperature readings, flush records and the source inspection sit in one timestamped place rather than in a folder nobody can find when the council asks.

Trade-offs and honest limits

The temptation off-mains is to treat the council’s drinking-water sampling as your whole compliance picture. It is not, a clean potability result says nothing about your cylinder. The opposite trap is paying for Legionella sampling you do not need; routine sampling is not required on most simple low-risk hot and cold systems, and your risk assessment, not a lab schedule, decides whether it adds anything [5].

This is general guidance, not a verdict on your borehole. Private supplies vary enormously, a single spring feeding one cottage is a different animal from a shared abstraction serving a holiday park, and only a competent, site-specific Legionella risk assessment under BS 8580-1, read alongside your local authority’s drinking-water requirements, tells you what your site needs [19].

FAQ

Does the local authority’s private water supply test cover Legionella?

No. Local-authority sampling under the Private Water Supplies Regulations 2016 checks drinking-water quality, chemistry and general microbiology at the point of use. Legionella control in your hot and cold systems is a separate duty you manage through your own risk assessment [3][6].

I have a borehole serving one holiday cottage. Do Legionella rules really apply?

Yes. The duty to assess and control Legionella risk follows the water system, not the supply source, and rented or let accommodation is explicitly within scope [7]. The assessment may well conclude the risk is low, but you still need to make and record that judgement.

Is borehole water more likely to grow Legionella than mains?

The source itself is not the issue, Legionella lives at low levels in most fresh groundwater anyway [13]. What matters is that untreated private water can carry more sediment and biofilm-feeding material into your storage, so tank cleanliness and temperature control deserve extra attention [6].

Next step

Pull your most recent local-authority drinking-water result and put it next to your Legionella risk assessment. If you only have one of the two, or the assessment is missing or older than your last big system change, that gap is today’s job. Logging the source inspection and your first set of temperatures in a single dated record is a sensible place to begin.

Sources

  1. HSE, ACoP L8 (2013), “Carrying out a risk assessment”, p.12. https://www.hse.gov.uk/pubns/books/l8.htm
  2. HSE, “Legionnaires’ disease, what you must do”. https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm
  3. HSE, “Testing and monitoring your water system for legionella”. https://www.hse.gov.uk/legionnaires/testing-monitoring-water-system.htm
  4. HSE, “Hot and cold water systems”. https://www.hse.gov.uk/legionnaires/hot-and-cold.htm
  5. HSE, “Legionella and landlords’ responsibilities”. https://www.hse.gov.uk/legionnaires/legionella-landlords-responsibilities.htm
  6. CDC, “How Legionella Spreads”. https://www.cdc.gov/legionella/causes/index.html
  7. BSI, BS 8580-1:2019, clause 4 (factors to be considered in the risk assessment). https://knowledge.bsigroup.com/products/water-quality-risk-assessments-for-legionella-control-code-of-practice-1
  8. Drinking Water Inspectorate, “Private Supply Legislation”. https://www.dwi.gov.uk/private-water-supplies/legislation-pws/
  9. Drinking Water Inspectorate, “Drinking Water 2024: private water supplies in Wales - introduction”. https://www.dwi.gov.uk/what-we-do/annual-report/drinking-water-2024/drinking-water-2024-private-water-supplies-in-wales/introduction/
  10. mygov.scot, “Registering, risk assessing and testing private water supplies”. https://www.mygov.scot/private-water-supplies/register-test-assess
  11. DAERA, “Private Water Supplies”. https://www.daera-ni.gov.uk/articles/private-water-supplies