It depends on how many swim practices I went to that day. I usually wash it twice a day, because of all the cholorine. I use a lot of conditioner in it though, to keep it from drying out.
Every day. I'm using this shampoo that makes my hair super silky and smooth and soft so I love using it. When I'm not in school I wash it every other day though. I don't want my hair to smell like..head.
I shower and wash my hair everday. I used to wash it and straighten it and then the next day straighten it again with no wash inbetween. My hair gets nasty if I don't wash it everyday.
In the Summer I have to wash it everyday, but the rest of the year I wash it one day yes and the following day a normal shower.
As said above, it is not really good to wash your hair everyday because it gets rid of "natural oils", but if you brush your hair a lot afterwards you stimulate your scalp and get more oils. =\