RN
The fantasy has the water doing something. It makes everything weightless, it washes away inhibition, and — in the version most people half-believe — it is somehow cleaner than a bed. None of that is how it works. Physically, submerging yourself changes three things, and two of them are working against you.
What water actually does
It removes lubrication. This is the single most consistent complaint and the source of most of the trouble downstream. Natural lubrication is not water-soluble by accident; it is a viscous fluid that surrounding water dilutes and carries off. Water is wet, but it is a poor lubricant — it has almost no viscosity and it does not stay where you put it. The result is more friction, not less, which means discomfort, micro-abrasion, and a materially higher chance of a condom tearing or slipping.
It changes buoyancy. Which is the one genuine advantage: positions that are hard to hold on land become easy, and weight stops being a limiting factor. This is why the idea is appealing in the first place and it is not nothing.
It introduces whatever is in the water. Chlorine, bromine, salt, or in a poorly maintained tub, bacteria. Mucous membrane is more permeable and more reactive than the skin on your back, and pool chemistry that your arms do not notice is a different proposition internally.
What water does not do
It is not a contraceptive. The exchange happens between two bodies in contact. The surrounding water is not involved in it, and the notion that chlorine intercepts anything is a folk belief with no mechanism behind it. Whatever the pregnancy risk would be on dry land is the pregnancy risk here.
It is not a barrier to infection. Same reasoning. Water does not sit between skin and skin at the point of contact, and disinfectant levels calibrated to keep a pool sanitary are nowhere near what would be needed to inactivate anything at the moment of transmission — nor would it get there in time if they were.
It does not make a condom unnecessary or safer. If anything the reverse: less lubrication and more slippage make a barrier method harder to use correctly, not easier.
The lubricant problem has one real answer
Water-based lubricant is the usual recommendation for everything else and it is the wrong choice here — it dissolves into the surrounding water within seconds. Silicone-based lubricant does not, because water has no effect on it. That is the one product-category fact worth knowing about water sex.
Oil is still out if a latex condom is involved, in water or anywhere else. Oil degrades latex, and that is not a preference issue.
Hot tubs specifically
Warm, aerated, low-turnover water is a good environment for Pseudomonas aeruginosa, and the itchy follicular rash it produces after a soak is common enough to have its own informal name. It comes from a tub whose disinfectant has been outpaced by the bather load — which is exactly the condition of a tub several people have been in for a while on a warm evening. This is a hygiene-of-that-specific-tub problem, not a hot-tubs-in-general problem, but you generally cannot tell by looking.
Heat is the other factor. Sustained wet heat raises scrotal temperature above the range sperm production requires, and reduced sperm counts following regular hot-tub or hot-bath use are well documented, with recovery over the following months once the exposure stops. Two points follow, and they cut in opposite directions. If you are trying to conceive, frequent long soaks are worth reconsidering. If you are not, this is emphatically not a form of contraception — the effect is partial, gradual, and nowhere near reliable.
Overheating in general deserves a mention. Extended immersion in hot water raises core temperature, drops blood pressure and causes dizziness, and alcohol makes every part of that worse. Sex adds exertion on top. The combination of heat, alcohol and water is the actual mechanism behind most hot-tub incidents that end badly.
Irritation, and the day after
People prone to urinary tract infections, bacterial vaginosis or thrush often report a flare after this, and the plausible reasons are unglamorous — friction, disrupted lubrication, warm water carrying whatever is on skin into places it does not normally go, and pool chemistry contacting tissue that reacts to it. It is not universal and it is not inevitable. It is common enough that if you already know you are susceptible, you can predict how this will go.
Anything that shows up afterwards — burning, discharge, a rash, pain on urinating — is worth a clinician rather than a week of cranberry juice and hope. Most of it is easily treated and none of it improves from being ignored.
The unromantic considerations
Shared water is other people's water. A public pool, a hotel tub, a rental spa: the hygiene question runs in both directions, and contaminating a shared facility is a real thing that happens, not a squeamish objection.
Then there is the legal dimension, which the fantasy never includes. Sex in a public or semi-public pool is an offence in most jurisdictions, and the consequences in some of them are considerably more durable than an infection. Hotel and resort staff are not neutral observers, and neither are the cameras.
Pool edges, ladders, tiled steps and jets are hard, sharp, and slippery in combination. Nobody plans to injure themselves in six inches of water, which is roughly why it happens.
Where this leaves it
A private tub you maintain, kept at a sensible temperature, without much alcohol, with silicone lubricant and a barrier method you have actually put on before getting in — that is a version of this with no particular problem attached to it. It bears very little resemblance to the fantasy, which usually involves a resort pool at 2am and several drinks.
The honest summary is that water adds buoyancy and takes away lubrication, and everything else people believe about it is either neutral or wrong. If the appeal is the setting, the shower, the tub edge or the poolside are all available and none of them involve being submerged.