The game is available for both Android and iOS (Apple iPhone/iPad).
Google Play Store link: Android
Apple App Store link: iOS
You can play Water Splash from HERE (this link will open a new window).
Also, you can find the game on Facebook Gameroom by searching "Water Splash".
If the link above does not work, it is also possible that you have Water Splash blocked. You can unblock Water Splash in your Privacy Settings.
Detailed instructions can be found in the following Facebook FAQ.