Spamming Healing Wave constantly isn't very mana effecient. Make sure that you keep earth shield on your tank and hit it with riptide when its up and lesser HW if the tank starts taking more dmg than rip can replace. Riptide is not expensive period. Also make sure you have your water shield on your Shammy. A few good click macros, found in the Wiki, with an "oh shit" heal macro should be ok.

Not everyone uses ISB