Same Pool, Different Day: Why Swimming Pool Water Feels Warm or Cold

Yesterday, before the rain even started, I was teaching in a small pool — one of the coldest pools I teach in each week. Small pools tend to fluctuate a little more than big ones (simply because they hold less water), and true enough, the moment we stepped in, all of us felt uncomfortably cold.

The kids shivered, so I immediately got them moving — big kicks, splashing, marching through the water. Movement helps raise base skin temperature, which makes the water feel more tolerable. Within minutes, the kids warmed up.

Just then, the toddlers pointed up: “It’s raining!”The two mums wondered whether the pool would now feel colder.

I told them, “Actually, the water should start feeling warmer soon.”And sure enough — it did.

This isn’t magic. It’s physiology, physics, and perception working together.

Ever wondered why swimming pool water feels warm or cold, even when the actual temperature barely changes? Here’s what’s really happening.

How the flip happens (at a glance)

Scenario	Your skin temp	Pool water (~29°C)	Sensation
Hot, sunny day	32–35°C	~29°C	Feels cool
Cool, rainy day	24–27°C	~29°C	Feels warm

👉 Same pool. Same temperature. Different skin temperature = different sensation.

This matches exactly the same science behind why pools feel cold under the hot Singapore sun.Nothing changes in the water — your body changes.

The real science behind why swimming pool water feels warm or cold

1) Water stays steady; your skin doesn’t

Water changes temperature slowly. Air doesn’t.Rain cools the air quickly, but the water stays almost the same — your own rainy-day thermometer readings proved this.

Small pools might shift slightly faster than large pools, but not dramatically.

2) Skin temperature drives perception

Your skin is the “sensor” your brain uses.

• On hot days, your skin is hotter than the pool, so the pool feels cold.

• On rainy days, your skin is colder than the pool, so the same water feels warm.

💡 Everyday example: On a rainy day, you naturally make your bath water hotter than you would on a sunny day. The bath hasn’t changed — your skin has. Pools follow the same principle.

3) Evaporation & wind shift comfort

Wind + wet skin = rapid cooling.Rain + humidity = slower evaporation, so your body loses heat more slowly.

When the rain started during my class, the kids’ discomfort eased quickly — because evaporation dropped.

4) Expectation and contrast

Warm-feeling water doesn’t mean the pool got hotter (or dirtier).It means you expected freezing water and instead got steady-temperature water, magnifying the sense of warmth.

This is the same phenomenon shown in the classic “lukewarm bowl” experiment with hot and cold hands.

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Swim Teacher’s rainy-day tips

• Prep the body: 60–90 seconds of simple movement before entering.

• Stay active in the pool: Movement keeps you feeling warm.

• Shield from wind: Use a poncho or towel during rest breaks.

• Warm exit: Dry off quickly and dress warmly after the swim.

☔ Safety note:Rain is fine.Thunder or lightning = leave the pool immediately.

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Try this at home

Two bowls (warm + cool), then both hands into lukewarm.

One hand feels “hot.” The other feels “cold.”

Same water — different baseline.

Same concept as the pool.

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Parent takeaway

The pool does not warm up in the rain.It stays steady — just like it stays steady on hot sunny days.What changes is your skin temperature, evaporation rate, wind exposure, and expectations.

This is why pools can feel cold in Singapore’s heat, and warm in Singapore’s rain — without contradicting each other.

References

Kenney, W. L., & Munce, T. A. (2003). Invited Review: Aging and human temperature regulation. Journal of Applied Physiology (1985), 95(6), 2598–2603. https://doi.org/10.1152/japplphysiol.00202.2003

Gagge, A. P., Stolwijk, J. A. J., & Hardy, J. D. (1967). Comfort and thermal sensations and associated physiological responses at various ambient temperatures. Environmental Research, 1(1), 1–20. https://doi.org/10.1016/0013-9351(67)90002-3

Heat balance when wearing protective clothing. (1999). The Annals of Occupational Hygiene, 43(5), 289–296. https://doi.org/10.1093/annhyg/43.5.289

Mower, G. D. (1976). Perceived intensity of peripheral thermal stimuli is independent of internal body temperature. Journal of Comparative & Physiological Psychology, 90(12), 1152–1155. https://doi.org/10.1037/h0077284

Parsons, K. (2014). Human Thermal Environments. https://doi.org/10.1201/b16750