why would I have water in my passenger side floor board ?

may be the A/C condensation drain tube stopped up.it's not the heater core,or windows would be fogging up and sweet smell would be present.you could smell antifreeze if it was the problem,also would be a color and slime feeling to touch it.

It's your heater core that's going out and it's not a easy fix either you have to have a repair shop fix this problem because the whole dashboard has to come off in order to replace it my husband had to do this to his car not a easy fix and very expensive to fix to sorry