Toeside waterstarts are great to do just after you've crashed riding toeside or just for general toeside riding fun.
Boardstart mastery. Toeside riding mastery.
To the Point:
Do a boardstart, but start with your weight over the toes of your front foot, which will become your back foot when you dive the kite.
Dive the kite more downwind than you would normally need to and prepared to point the opposite end of the kiteboard towards the kite than you normally would. Meaning, if you dive the kite downwind to the left, your right foot is going to be your front foot. If you dive the kite downwind to the right, your left foot is going to be your front foot.
After you dive the kite and are on top of the board, set your toeside edge by shifting your weight over you toes, twisting your front shoulder and hip upwind, and lastly, leaning forward.
If you are sinking immediately after your start, practice riding toeside more by doing toeside transitions, or 180s to toeside. Once you've mastered toeside riding, toeside waterstarts will be easy.