This happened when I was 20
I was 20 and living in a flat with 2 friends. It was a hot summers day, and I came home from work hot & sweaty and looking forward to a cool shower.
I turned the shower on and started to take my clothes off when the showerhead just fell off and onto the showerbox floor. I tried to fix it but it was totally broken and would not re-attach to the pipe sticking out of the wall. In need of a shower, I turned it on and stood under the constant stream of cool water spurting from the pipe.
I soaped myself and washed my hair and then while rinsing myself off, my penis went under the stream of gushing water, and it felt so good that I stood there with the water falling onto the base of my now hardening cock.
I started breathing harder with excitement and decided to stay there to see what would happen. The water was falling in a hard stream, which felt great while it was falling onto the base & shaft of my cock, but when it hit the glans it was too powerful and almost hurt. I pulled my foreskin up over the head of my cock as far as I could which lessened the impact of the water against my glans and, again held under the flow. The feeling was so, so intense and I was so excited that I came in about 30 seconds with the most powerful orgasm I think I had ever had. My legs went weak and I had to lean against the wall until I regained my strength.
I have replicated this experience a few times since then, but have never had the same level of enjoyment as I had that day.