---
title: "Who actually controls the cooling tower: the responsible person and water-treatment contractor split"
source_url: https://legionella.io/articles/cooling-tower-responsible-person-vs-water-treatment-contractor/
canonical_url: https://legionella.io/articles/cooling-tower-responsible-person-vs-water-treatment-contractor/
pillar: "Common Failures & Enforcement"
summary: "You can outsource cooling-tower water treatment but not the legal duty. See exactly what stays with the responsible person and what the contractor actually owns."
primary_keyword: "cooling tower responsible person"
date_published: 2026-06-27
date_reviewed: 2026-06-27
author: "Legionella.io editorial team (REMOTE TECH LTD)"
reviewed_against: "HSE L8 and HSG274 guidance"
region: "United Kingdom"
license: "CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Quote, adapt or republish with attribution to REMOTE TECH LTD and a link to source_url."
license_url: https://creativecommons.org/licenses/by/4.0/
---

# Who actually controls the cooling tower: the responsible person and water-treatment contractor split

The most expensive cooling-tower failure rarely starts at the tower. It starts in a meeting where someone says "the water treatment company has it covered" and everyone moves on. The contractor does what the contract pays for. The legal duty never left the building's duty holder. That gap is where loss of control hides.

A cooling tower is the highest-consequence water system most sites will ever run, because it can release a fine aerosol beyond the building line. Yet its day-to-day chemistry is almost always outsourced, and outsourcing the task quietly gets mistaken for outsourcing the responsibility. It is not the same thing.

This piece maps the split: what genuinely stays with the responsible person, what the contractor actually delivers, and how to read a service visit so a drift toward out-of-control does not pass unnoticed between two parties who each assume the other is watching.

## Myth versus reality: who owns what

The table below is the article in one view. Pin it next to the service file.

| The myth | The reality |
|---|---|
| "We have a water treatment contract, so the tower is compliant." | A contract is a control measure, not compliance. The duty to assess and manage the risk rests with the duty holder and cannot be signed away by appointing a contractor [1]. |
| "The contractor is the responsible person." | The responsible person is an appointment the duty holder makes from within their own control, usually a named manager. A contractor delivers a service to that person; they do not become it [1]. |
| "No phone call means no problem." | Silence is not assurance. A trend creeping toward an action level can sit in the visit sheets for weeks if nobody on the client side reads them [2]. |
| "Signing the engineer's sheet is reviewing the results." | A signature confirms a visit happened. Reviewing means checking the readings against the scheme's control limits and acting when they drift [2]. |
| "Acting on an out-of-control result is the contractor's job." | The contractor advises and can carry out remedial work; deciding, resourcing and, where relevant, notifying remain the duty holder's call [1][2]. |

## "The contract covers it"

A service contract buys attendance, dosing, sampling and a report. It does not buy away the duty. Health and safety law places the obligation to manage the risk on the person in control of the premises, and that obligation stays put when a contractor walks in. ACoP L8 is explicit that responsibilities are appointed and managed, not abolished, by bringing in help [1].

The practical test: if the local authority or HSE asked tomorrow who decided the monitoring frequencies, who reviews the results, and who would shut the tower down on a bad sample, the honest answer must be a named person on your side, not "the contractor". A cooling tower is also typically a notifiable device, and that notification duty sits with the person in control of the premises, not the contractor servicing it.

## "The contractor is the responsible person"

The responsible person is a role you appoint and empower from within your own organisation: someone with enough authority and competence to take decisions and make resources available [1]. A water-treatment contractor is a specialist supplier to that person. They can be highly competent. They can run the chemistry better than you ever could, and they are still the supplier, not the accountable officer.

Where this goes wrong is the empty chair. A site outsources everything, never appoints an internal responsible person, and assumes the contractor occupies the role by default. They do not, and an auditor will find the gap quickly. Choosing a supplier who works to a recognised service-provider code of conduct raises the floor on quality, but it does not fill that chair for you [3].

## "If there were a problem, they'd tell us"

This is the dangerous one, because it feels reasonable. Most reputable contractors will flag a serious excursion. But routine drift, conductivity climbing, a biocide residual slipping, a dip-slide trending the wrong way, an early Legionella count that warrants a resample, can read as "within tolerance for now" on a busy engineer's sheet and never trigger a call. If nobody on the client side is reading the trend, the first time you learn control was slipping may be the visit where it has already gone.

The fix is unglamorous: someone competent reviews each visit report against the written scheme of control, looks at the direction of travel rather than the single value, and records that the review happened. The detail of which parameters and action levels to watch belongs in your scheme, see the sibling pieces on building a cooling-tower control scheme and on responding to Legionella sample results, but the act of reviewing is a duty-holder task, full stop [2].

## "Signing the sheet is enough"

A signature at the end of a visit confirms an engineer attended and you saw them. It is not a review, and treating it as one is how out-of-control results get countersigned into the file. Reviewing means comparing what was measured to the limits your risk assessment set, asking whether anything is trending toward an action level, and triggering a defined response if it is. HSG274 Part 1 frames the cooling-tower regime around exactly this loop of monitoring, recording and acting on results, the recording without the acting is half a system [2].

## How to read a service visit sheet without being a chemist

You do not need a water-treatment qualification to spot trouble; you need to read three things in order.

- **Were the right things measured, at the agreed frequency?** Compare the visit against your scheme. A skipped parameter or a stretched interval is itself a finding.
- **Is anything outside its control limit, or trending toward one?** Look across the last several visits, not just today's. Direction matters more than any single reading.
- **If something was out of range, what was done, by whom, and is it closed?** An out-of-control reading with no recorded action, or an "action recommended" with no client decision against it, is an open loop you own.

That review, and the decision that follows an excursion, is the part of the job that cannot be delegated to the people you are paying to do the chemistry. Build it into a named person's calendar, not the contractor's.

This is general guidance on the accountability split, not a substitute for your own arrangements. The control parameters, action levels, monitoring frequencies and the precise division of duties for your tower must come from a competent, site-specific Legionella risk assessment and written scheme of control, written for your plant, your occupancy and your contract, by someone competent to do it. Nothing here is legal advice.

## FAQ

### Can we appoint our water-treatment contractor as our responsible person?

You can give a competent external person a defined role, but the duty holder retains accountability and must be satisfied that whoever holds it has the authority, competence and time to do it [1]. In practice the responsible person is best held internally, with the contractor as a specialist supplier to them. If you do place any duties externally, define them in writing and confirm the appointee accepts and is capable of them, an unwritten assumption that "the contractor is the RP" is exactly the failure that gets found.

### Our contractor sends detailed reports we never read, is that a problem?

Yes. Unread reports are arguably worse than none, because they create a paper trail showing data arrived and nobody acted on a developing trend. The recording duty in HSG274 only protects you if it is paired with a review-and-act duty on your side [2]. Put a recurring review of each visit into a named person's responsibilities and record that the review took place.

### If a Legionella sample comes back high, whose job is it to respond?

The contractor will usually flag it and can carry out remedial work, but the decision to act, the resourcing of that action and any consequent notification or shutdown sit with the duty holder and responsible person [1][2]. Agree the escalation route in advance, who is phoned, who decides, against what action levels, so a high result triggers a defined response rather than a debate about whose call it is.

### What should our contract actually specify about scope?

Enough that there is no grey area. State which parameters are monitored and at what frequency, what the contractor does on an out-of-range result versus what they refer back to you, what reporting you receive and when, and who is responsible for review and for notification. A scope that lists only "monthly visit and dose" leaves the accountability boundary undefined, which is where things fall through.

## Related reading

- [A worked cooling tower control scheme](https://legionella.io/articles/cooling-tower-control-scheme-worked-example/)
- [Cooling tower Legionella sampling and action levels](https://legionella.io/articles/cooling-tower-legionella-sampling-action-levels/)
- [Working with contractors and ensuring Legionella compliance](https://legionella.io/articles/working-with-contractors-ensuring-legionella-compliance/)
- [Written scheme of control template and worked example](https://legionella.io/articles/written-scheme-of-control-template-and-worked-example-regulation-8-acop-l8/)

## Sources

[1] HSE, ACoP L8 (2013), “Managing the risk: management responsibilities, training and competence”, p.14. https://www.hse.gov.uk/pubns/books/l8.htm
[2] HSE, HSG274 Part 1 (2024), “Requirements of a cooling water treatment programme”, p.17. https://www.hse.gov.uk/pubns/books/hsg274.htm
[3] Legionella Control Association, "Code of Conduct for Service Providers". https://www.legionellacontrolassociation.co.uk/