Water-Venture Pasir Ris is located at 125 Elias Road. There is only one bus service that plys that route and the frequency can be quite slow at around 20minutes or so.
To get there, you can take bus service 403 from Pasir Ris Interchange and alight after the roundabout in Pasir Ris Park.
Personally, I prefer to cycle there from my home in Hougang.