How to make Instant Hot Chocolate Taste Less Watery

I can think of four possible fixes. One is simply, use less water - a smaller amount of a richer drink may well be preferable to a larger amount of a watery drink. Another is the reverse, use more mix, which uses two packets (if not all of the second is necessary, you might share with someone else who wants extra, save it for next time, or simply discard).

Third option would be to add a pinch of salt. It can help balance the flavors (a pinch isn't enough to make it not-sweet), and it's commonly described that less salt can make something taste "watery", and adding a touch of salt makes things taste more balanced. It will change the flavor a bit, but not necessarily badly.

Fourth option is to add stuff. Sugar, creamer powder, spices (possibly brought from home), whatever pleases you - and some of which might already be present for doctoring coffee. Any of these options should add some flavor, changing the taste but perhaps not badly. I wouldn't recommend milk, since (as you mention) it has enough liquid it can dilute the flavors, but powdered flavorings might help (and not dilute). Or you might even try keeping on hand a candy to dissolve in your drink (peppermint round, wrapped caramel) the heat and water should let it dissolve a burst of flavor into your drink. Again, flavored, but not necessarily bad.

The first solution is to use two sachets per cup instead of one. The second is to ditch the sachets and simply use chocolate. The sachets themselves are a mixture of cocoa powder with fillers, mostly sugar, but real deep chocolate taste only comes from chocolate.

For example, Rausch in Berlin serves hot chocolate made of about 60% dark chocolate to 40% hot water. That's on the high side for sure, but it does pack a punch.

I have found that different brands of hot chocolate drinks have varying chocolate flavor intensities (some are much stronger than others) Try using the different ones that are availble in your supermarkets, shops and online In the United States, I found that Ghirardelli Chocolate Premium Hot Cocoa - Double Chocolate is one that provided the most intense chocolate flavor

I used to be in the same predicament as you and I used 1/2 liquid coffee creamer and 1/2 boiling hot water and then it tasted just right. (Both temperature and taste)

I was told off by the boss after a while though as one colleague and me ended up using 80% of the creamer in the office and it took a bit of time filling half a cup with the tiny coffee creamers we had.