Well, I have a lower carb count, maybe I calculated wrong. Did yours end up making quite a bit?
As far as the water, I use heavy cream, which makes it way to fatty tasting to me so thats why I add the water. When I whip up heavy cream to a real stiff point, it tastes like sweet creamy fat!! When I add water, it spreads it out more and not so fatty tasting.
On my carb count, when I use whipped cream cheese, that has less than 1 carb per 2 tbls. I figure I use about 6 Tbls, give or take...which in turn is approx (at .5 carbs per 2 Tbls) 1.5 carbs for the cream cheese alone. My sour cream is 1 carb per 2 Tbls...figuring I use about 4 Tbls...that is 2 carbs for the sour cream. Heavy cream says 0 carbs so I figure that at .6 per serving...which is 1 Tbs....there are 6 T for 1/2 c.....so for cream I figure 3.6 carbs.

Cream cheese.......1.5
Sour cream............2
Heavy cream.........3.6
Splenda.................3
Total carbs............10.1

And I cant even eat the whole bowl......It usually makes enough for half after lunch and half after dinner.