How do i post my water......

If you do a search for 'water', one of the items listed will be 'water, municiple', which is plain old tap water. If that's what you drink, select it and add it to your Favorites. Bottled water is probably on the list, too. Just select the type of water you drink.

I find it easiest just to keep track throughout the day of how much water I drink, and then list the total amount as "Snack 3" in my My P.L.A.N. entry for the day. You might find a different way that works better for you.