I was 13 she was 15 at the time
I just read a story on here called 'Water Jet Fun' and it brought back so many memories of when my sister would let me watch her under water while she was doing the very same thing.
I always knew when she was really horny because she would come and find me to ask me if I wanted to go swimming. And I always knew what she meant when she asked that way. We would get our suits on, jump in, swim around awhile, and eventually she would make her way over to the steps where one of the jets was located on the side of the pool wall. She would position herself in front of it and pull the front of her bathing suit bottoms to the side, exposing her pussy to the flowing water. After a minute or so she would ask me if I wanted to watch. I would put the swim mask on and hold my breath for as long as I could to get many good long looks. It was wonderful to see her clit being vibrated by the water stream. After a couple of times of coming up to catch my breath she would tell me I could touch, if I wanted too. Of course I wanted too! I would play with her pussy with my fingers, feeling all the folds. Soon she would tell me to put my fingers inside. I would put two or three inside and could feel her muscles flexing on them. Soon after she would buck and hump my hand until she shuttered in an orgasm.
We had many fun times in the pool and some out. But those are for another time.