Legionella testing kits

Updated 12 September 2026

"Legionella testing kit" covers several distinct products, each suited to a different purpose. For duty holders, the most important distinction is between kits that produce evidence that will stand up to inspection and kits that do not. This page covers the main types, their limitations, and when each is appropriate.

UKAS-accredited culture sample kits

These are the standard kits supplied by legionella testing laboratories. The kit typically contains:

• A sterile bottle (usually 500 ml, 750 ml, or 1 litre) containing a small quantity of sodium thiosulphate to neutralise residual chlorine
• A cold pack for return shipping
• A padded envelope or courier box
• A pre-paid courier return label
• A sample information form to record outlet reference, temperature, date, and operator

The sample is taken at your premises, packed with the cold pack, and returned to the laboratory within 24 to 48 hours. The laboratory cultures the sample for ten days using ISO 11731 and reports the result as colony-forming units per litre (cfu/L) for each legionella species found. Typical cost per sample is 30 to 80 pounds including the kit, the courier return, and the analysis.

This is the kit type to use for any sampling that will form part of the compliance record. Results from a UKAS-accredited laboratory are legally defensible; results from non-accredited alternatives are not.

Dip slides

A dip slide is a small paddle coated on both sides with agar. One side grows total viable bacteria, the other grows yeasts and moulds. The slide is dipped into the water sample, closed in a sterile container, incubated at 30°C for 24 to 48 hours, and the colony growth visually compared to a reference chart.

Dip slides are cheap (around 3 to 10 pounds each) and fast. They are widely used in cooling tower monitoring to track changes in the total bacterial population between scheduled laboratory samples. A sudden rise in dip slide count is a trigger to investigate and, if necessary, to take a laboratory sample.

Important limitations:

• Dip slides do not identify legionella specifically. A clean dip slide is not evidence that legionella is absent; a dirty one is not evidence that legionella is present.
• Results are semi-quantitative at best, read by eye against a reference chart.
• They are not UKAS-accredited and cannot be used as compliance evidence.

Dip slides have a legitimate place in routine cooling tower and closed-loop system monitoring as an indicator of general bacterial control. They are not a substitute for laboratory sampling.

Rapid PCR kits

Polymerase chain reaction (PCR) kits detect legionella DNA in a water sample, returning a result in a matter of hours. They are particularly useful in outbreak investigations where a traditional ten-day culture is too slow.

Two limitations to bear in mind:

• PCR detects DNA whether the organism is alive or dead. A positive PCR result after a recent disinfection may reflect dead cells rather than an ongoing risk.
• PCR results are not always accepted in the UK as the primary compliance sample. Most duty holders use PCR as a rapid screen and confirm with culture.

Typical cost per PCR sample is 80 to 150 pounds.

Home self-test kits

A number of consumer-grade "legionella home test" kits are marketed online, often to landlords who have been advised they need a legionella test. These typically work by one of two methods:

• Antigen-based lateral flow (similar to a COVID test), which gives a yes or no result
• Dip slide style tests that measure total bacteria

Neither of these is a substitute for a UKAS-accredited laboratory sample. They are not accredited, their sensitivity is not comparable to ISO 11731 culture, and their results are not accepted as compliance evidence.

For a single domestic let, the HSE position is clear: annual legionella sampling is not normally required, and a risk assessment based on temperature and flushing is sufficient. If you have been told by a letting agent or insurer that you need a "legionella test", ask exactly what they want. Usually they want a copy of the written risk assessment, not a laboratory sample.

What to include in a sampling kit order

For premises that do need to sample, order kits with enough spare capacity to handle contingencies. A typical quarterly order for a medium commercial building might include:

• Six to twelve sample bottles for the scheduled sentinel outlets
• Two to four spare bottles for opportunistic sampling
• One or two bottles specifically for resampling if a previous result was positive
• Dip slides if cooling tower monitoring is included

Pricing gets more favourable per sample at higher volumes, so an annual order with staggered shipment is often cheaper than ordering quarterly.