The "explosion" that would outcome might simply be the result of the actual thermite causing the drinking water in order to quickly range from the actual solid to the gas state--basically, dispersal of fragments due to fast gasoline growth.
This makes a lot of the thermite to be wasted, as much of the mix is going to be scattered prior to it ignites.
Burning up thermite won't trigger drinking water to split up into it's element elements, air as well as hydrogen.
I am not sure the reason why you may wish to add a binder to thermite, rather than merely limiting it. I've not tried it, but I wonder in the event that mixing it with a bit of dissolved parrafin may work.