Dude. Get it right! Is a small clear bubble not a small blister? Same thing. It is just a blister man. Many people from time to time have a weaker immune for a bit and thus react to polyester in the form of a small blister. There is no STD that is like that. You are fine. Could be from masterbation friction the day before or 2 or 3, and you didn't notice right off. Relax man. You are fine.
I never heard the term water spot. This is starting to sound more like an irritation and nothing more to me. But I am not a doctor either. Especially where there is only one spot and it on on your penis end. A part that rubs when you play sport. Friction can cause eruptions. You do seem a bit too nervous about it. Maybe you have cause but it is not too alarming to my knowledge. Now you say it didn't really itch, not a blister, not sore. Which it turning away from what I thought it could be. If it is an irritaion and you stop the culprit "running around with loose shorts so it moves around a lot, then it should get better.
It start with a small un-noticable irritation. And then hot water inflames it, causing a bump.
Although the way you describe the bump, it may be something else. It is not the classic symptom. But many people break out in a different form. And many inflamed areas become more sensitive to light allergens. Still you are the only one I replied to that I am not real sure. Some people get tiny blister, or many. Like me. Some people get a red spots, I get them sometimes, some get bump, same color as the skin there, and some get a rash. All these reactions are from the same thing.
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