Wet vs Dry Testing on Pool Surrounds

Wet is binding for pools — full stop

For almost any other UK environment, the wet/dry decision is contextual: a warehouse floor away from loading bays may be a dry-only environment; a retail entrance is a wet environment. For pools, the question doesn't arise. Pool surrounds, steps, ladder approaches, hydrotherapy ramps, shower zones and changing-room transitions are wet at all times during operating hours, and intermittently wet at all other times.

Reporting only dry PTV for a pool surround would be misleading and would not satisfy any UK pool specification. Standard practice is to report wet PTV with brief dry context where the wet/dry delta is informative diagnostically.

The standard wet contaminant

BS EN 16165 Annex C specifies clean tap water at ambient temperature as the standard wet contaminant. For pool testing, this is appropriate because the dominant contaminant on pool surrounds is pool water, which approximates clean water in friction terms despite its chemical content (chlorine, salt, calcium hardness adjustments). The pendulum test is reproducible across UK pool sites because the test contaminant is the same everywhere, regardless of the specific pool's plant chemistry.

Pool plant chemistry and the test

Pool water itself differs slightly from clean tap water. Standard chlorinated pool water with normal calcium hardness produces PTV results within 1–2 points of clean tap water on most surrounds — within the standard test variation. For most operational testing, clean tap water is the right contaminant.

For specific forensic questions where the operator's plant chemistry is unusually aggressive (very high chlorine, salt cells, low pH excursions), supplementary testing using actual pool water can identify whether plant chemistry is contributing to the friction picture. This is a non-standard test and the report states the contaminant explicitly.

Sun cream, body oil, soap — when they matter

Beyond water, pool surrounds frequently carry biological contaminants from users:

• Sun cream — particularly relevant outdoors and at hotel pools; oil-based formulations transfer to surround tile and accumulate
• Body oils and emollients — natural skin oils transfer over time; emollient-based skincare products amplify this
• Soap residue — from showers and from after-pool rinsing; reduces friction
• Hair conditioner residue — particularly in changing-room shower zones

For periodic compliance testing, water is the right standard contaminant. For forensic post-incident testing, supplementary contamination testing with the specific substance reportedly present at the time of the incident can produce additional evidence. The supplementary tests are clearly labelled as non-standard and reported separately from the water-wet PTV.

The wet/dry delta as a diagnostic

The size of the wet-to-dry PTV reduction is itself diagnostic for pool surrounds:

• Small delta (5–15 points) — surround texture is providing real wet friction; well-selected surface for the environment
• Moderate delta (15–30 points) — typical for mid-spec pool surrounds; acceptable if wet value remains above 36
• Large delta (30+ points) — surround relies heavily on dry friction; wet performance may be borderline even if absolute wet PTV is technically acceptable
• Very large delta (50+ points) — almost always indicates a polished surround with negligible wet friction; high slip risk in any wet condition

Reporting the wet result

Compliant pool reports show wet PTV for every test location, in every test direction, with the dry result for context where it adds diagnostic value. The wet result against the HSE bands is the headline; the wet/dry delta is the supporting context.