Yes, water is always good.

B12 is only very minimally absorbed passively in the GI tract.
People who use it under the tongue, swallow the B12 dissolved in the saliva and it becomes oral after all.

But using the high doses 1mg or 5mg insures enough is absorbed ...about 1% to make it successful. We absorb normally from animal sourced foods (meat, eggs, dairy, seafood) from 2-4 micrograms a day if intrinsic factor is working in the stomach and if you have enough acid there.

From 1mg oral tablet you may absorb up to 10 micrograms a day, IF you take it on an empty stomach, so food and fiber will not sponge it up and block absorption. It has been shown that microgram doses of some drugs like thyroid hormone are also affected by the presence of food. So B12 should be taken when the stomach and intestine are empty, and for at least an hour before any meal or is consumed. The main studies on B12 absorption were done this way, but the supplement manufacturers don't really read the studies. B12 is one of the few vitamins that must be taken this way, because of its uniquely tiny dose size.