Spa pools and hot tubs: what HSG282 actually asks of you

Two questions get asked about a commercial hot tub, and both have short answers. Am I in scope? You are if the tub is run as a business or shared beyond a single household. What do I actually have to do? Continuous disinfection through an inline feeder, chemistry tested at least twice a day, and a sampling routine on top, because warm aerated water is the most efficient legionella generator you will find anywhere on a site.

HSG282 is the HSE standard, published in 2017, for spa-pool systems. It covers everything from a commercial hot tub to a hydrotherapy pool, and it is blunt about why these sit at the top of the risk pile. Water held around 36°C, heavy aeration throwing aerosol into the breathing zone, and a bather load that keeps feeding organic matter into the water. That is close to a laboratory recipe for legionella and Pseudomonas, which is why the regime is heavier than anything you run on a normal hot and cold system.

Whether your tub is in scope is a financial question, not a property one

The mistake is to look at the building. A hot tub that looks domestic, sitting on the decking of a holiday cottage, must be domestic, surely. It isn't. Scope turns on financial gain and multiple users, not the type of premises or how the tub looks.

In scope: any spa or hot tub used as part of a business, or available to more than one household. Holiday lets and lodges, caravans and holiday parks, hotels, gyms and leisure centres, the display spa bubbling away on a showroom floor, hydrotherapy pools. Out of scope: a privately owned domestic spa, used by one household, with no financial gain attached.

The holiday-cottage case is the one worth holding onto, because it catches people out. A single family uses the tub during their week, so it feels private. But the cottage is let to successive guests for money, and that makes it commercial and in scope. One family in the water at a time, still a commercial system, still HSG282.

The routine regime

HSG282 describes a continuous-disinfection regime, not a dose-and-hope one. Treat the exact figures below as commonly cited numbers rather than hard law. The standard is the authority, so go to HSG282 itself for the definitive values and let your risk assessment set the ones that apply to your system.

Sanitiser goes in through an inline feeder, never hand-dosed into occupied water. Chlorine typically sits around 3 to 5 mg/l, inside a working range of 1 to 10. Bromine runs a little higher, commonly 4 to 6 mg/l within a range of 2 to 12. pH is held between 7.0 and 7.6, because chlorine disinfection falls off sharply as pH climbs. Water temperature sits around 35.5 to 36°C and should not exceed 38°C.

The testing and dilution routine that sits on top:

The dilution figure is the one operators tend to skip. Around 30 litres of fresh water per bather keeps dissolved solids and organic load from climbing to the point where the sanitiser is fighting a losing battle. Skip it and the chemistry looks fine on the test strip right up until the microbiology comes back dirty.

The action levels that close a spa

Chemistry tells you the treatment is working. Microbiology tells you whether it worked. A source reproducing the HSG282 action levels sets them out like this:

The number to internalise is legionella over 1,000 cfu/l. That is not a review-the-programme number, the way a borderline aerobic count might be. It is a get-the-public-out-of-the-water-today number, and the sequence after it (closure, shock dose, resample, investigate why) is not optional. Pseudomonas over 50 cfu/100 ml lands in the same place, closure and shock dosing, and it is the organism most likely to catch a well-run spa out, because it thrives in the biofilm inside pipework and filters that the free chlorine reading never sees.

This is why the twice-daily chemistry matters so much on a spa specifically. On a normal building hot and cold system, monthly temperatures carry most of the monitoring load. On a spa, the water is deliberately held in the danger band, so the only thing standing between the bathers and a colonised pool is a disinfectant residual that has to be checked and corrected twice a day, every day it runs. Miss a day and you have no evidence the barrier was up.

Where the spa sits in the wider programme

A spa is rarely the only water system on a site. The same building has a hot and cold system underneath it with its own monitoring cadence, and the changing-room showers around the pool are exactly the little-used outlets that need flushing and evidence per outlet. The spa regime above is an addition to all of that, not a replacement for it. If you are building the site's overall duty picture, the ACoP L8 compliance checklist is the frame the spa hangs inside.

What is different about the spa is the rhythm. Twice a day, every day in use, is a cadence a monthly-visit contractor cannot cover alone. Someone on site has to take and record the readings between your visits, and the value of your service is partly in setting that up so the log is complete and the out-of-range results actually get acted on rather than written down and forgotten.

That recording problem is what the BlueWave engineer app is built for on the spa specifically. The twice-daily sanitiser and pH readings are captured on site against the individual spa as an asset, so a chlorine result that drops below the range flags at the point of entry rather than surfacing a month later when the microbiology comes back. On-site staff record on the same form your engineer uses, the whole log lands in one place, and the quarterly legionella result reads against the same asset history as the daily chemistry. The record is complete because it was never split across a paper log and a spreadsheet in the first place.

If you take one thing from HSG282, make it the scope rule, because it is the one that costs money when it is wrong. A holiday-let operator who assumes their single hot tub is domestic has no regime, no records and no defence, right up until an outbreak investigation asks for two years of chemistry logs. The tub is in scope the day it is let for money. Everything else follows from getting that first line right.