It depends on the kind of cocoa product I’m using. If it’s the pre-mixed instant powder, (since it’s a mix of powdered milk, cocoa and sugar) I use water. If it’s cocoa powder, I use milk. If it’s unsweetened chocolate, I also use milk, and vanilla extract. (The last two links are to recipie pages.)
MILK!
fercrissake
I do mine with 50/50 milk & half-and-half, plus straight cocoa powder & sugar. I use about twice as much cocoa as Podkayne; it should be thick as well as flavorful. If it doesn’t have some choco-sludge in the bottom, well you shorted the cocoa.
The premixed crap is just that.
Marshmallows are sacrilege, although a smidgen of real whipped cream is OK.
For a real neat treat, make your usual hot chocolate and add 1 tsp to 1 tbsp of malted milk powder. It’ll taste kinda funny for the first sip, then you’ll be hooked.
One of many American brands I hear mentioned all the time but have no idea what it is.
Half and half is a kind of light cream. It’s not as thin as milk, but not as high fat as full cream.
Ahh, ‘semi-skimmed’ then.
I make my hot chocolate with semi-skimmed
Not exactly, it’s half milk, and half cream. 
Good stuff in coffee, not as sinful as pure cream, but with more flavor than milk.
I use powdered Swiss Miss mix (milk chocolate flavor). Two-thirds boiling hot milk, two heaping spoonfuls of mix, top the mug off with milk. Just-milk cocoa seems too thin, and all-milk cocoa is too much effort. My mom made it with some milk, I make it with some milk, I will teach my children to make it with some milk, and thus it continues throughout the ages.
If I’m making Swiss Miss, I’ll use hot water; but in the more likely event I’m making hot cocoa, either Ghiradelli, or Cadbury’s, or made from scratch using Hershey’s cocoa, then milk is a must.
I didn’t even know you could use water for making hot chocolate. Gross!
I’m assuming that answers the question?
I’ve made cocoa from scratch using Hershey powder and using actual squares of chocolate melted in hot milk over the stove. I much prefer Swiss Miss, thanks.
Always had it with water, until someone served it to me from milk once… every time I’ve had it with water since, it has tasted so… watery? Certainly nowhere near as satisfying.
I usually do a good sized mug of milk (so probably a cup and a third’s worth), about three tsp of cocoa powder, a couple T of sugar, and maybe a dash of vanilla. There’s a very similar recipe on the side of the Hershey’s Cocoa Powder box, actually. Delicious.
Strictly moo-juice. No water shall enter a mug with chocolate in this house!
Last night I tried it a bit different- I used the chocolate powder, milk, sugar, but also added some mocha coffee creamer. Good stuff!
Heathen that I am, though, I put a dollop of Cool Whip on top, not marshmallows. The coolness with the warmth is nummy.
Milk!
I’ve always used water, as have most of the people that I know. But tonight, I had the epiphany of taking some of my old Christmas chocolate and adding it in. Mmmm. Ultra-Cocoa™!
As above: if it’s a mix, water (and then I add milk afterwards, as you would to coffee.) If it’s the Paladín mix I bought in Spain and have been hoarding preciously (it’s not just hot chocolate, it’s chocolate – thick as pudding and hot as sin), it’s hot milk. If it were Fry’s Cocoa (which always makes me think of that time when they found those Antarctic explorers frozen to death with their supply of Fry’s still intact and fresh), it would be milk (and sugar, as it’s not sweetened).
You only use water with those Swiss-Miss type instant hot chocolate mixes which already contain powdered milk in them. I mean, the idea of cocoa powder or chocolate syrup with water is just plain revolting. Real hot chocolate is a milk-based drink, of course.
Even then, I like making my instant hot chocolate with milk, if possible. It’s just much richer and creamier.
I’ll use regular instant hot cocoa mix, but I’ll always punch it up with either milk or flavored coffee creamer (White Chocolate Raspberry was best, but they don’t sell it anymore, so I go with either Irish Cream or Mocha flavored creamers).
When it gets really cold out, I’ll use real Irish Cream, Kahlua, or creme de menthe.
And a dollop (or two) of Cool Whip on top beats all hell out of plain ol’ marshmallows. With chocolate sprinkles and a maraschino cherry on top.
I use milk, whether I make it with mix or cocoa powder. I also add a little more milk afterward. Sometimes I put a bit of chocolate from a bar, one Hershey Kiss, or stir it with a candy cane. Yummy.
Milk.
[slight hijack]
I sent bedmate down to the kitchen to get me a glass of cordial the other night, and, unable to find the requisite concentrate, he decided to stick some Chocolate Topping into a glass of water instead. He very proudly presented it to me to drink…I nearly puked of course. 
[/hijack]