I'm using a multi fuel stove (MSR Dragonfly) for a 10 day ski tour, how much fuel should I allow to provide sufficient water for cooking and drinking. Meals will be mostly dehydrated just-add-water types. I'm not expecting to need much (any) for washing!
I've heard from numerable places that when climbing Denali, plan on a cup (About .25 L) of white gas per person per day. I would say that this should be a good rule of thumb for your trip as well. You might be able to get away with a bit less, but this is at least a good rule of thumb.
You probably won't need this much, but it's a good rule of thumb still. Denali has additional challeneges, with the altitude it has, and from what I've heard, most climbers come down with extra gas.
10 inches of snow will give you 1 inch of water. Lets say you need to fill your container half way full to get a cup of water, well that means you're going to have to fill it full 5 times to get that cup, melting it each time. I usually budget about 4-5 times the fuel in the winter than I use in the summer.
You can speed things up by pouring a bit of water in the bottom to begin with, and it'll also avoid the bottom of your pan scorching.