The equipment needed depends on what you want to do with your photographing.
I guess I all in all have spent about foutrhy hours photographing UW - rugby.
Some of hte results are presented here: https://runehaldor.f...it=30&offset=30
If you're taking photos in the surface while the players are exercising, a ewa-marine or similar bag might be completly ok. If you want to swim a bit deeper, a decent underwater housing might be a good idea. A few meters below surface without using strobes manual wite ballance about 9000 K is a good start.
If you are taking photos during a match, my experience is that scuba equipment is a good idea. The easiest is to get air fronm an extended regulator with the bottles on land. Normally this equipment is just aviable for the referee, so full scuba equipment is needed. Quite often, I find the side with the best natural light and wait for the one team to attac. Especially male teams are quick and you need strobes to get sharp pictures. It is also a good idea to observe a few matches or to play for a while yourself to understand enough of the game to know when to shoot.