you can't really rebuild the water pump as such, also if you havn't done your 100k service, then do that too at the same time cos 9 times out of 10 you need to take the timing belt off, but some people have done it without taking the belt off...
but theres a little hole at the front of the water pump which you can see from underneath, it usually leaks from there when the seal inside is gone, its like a breather hole or something like that, but keep an eye on the coolant cos it'll drain quickly