Like everything in diving, all in moderation!Fair enough - just many people are so worried about underhyrdation and potential risks associated with that, that they can overdo it the other way which could also have risks. Just be properly hydrated.
I know that on a boat there's plenty of distractions and never enough tea (albeit that's a diuretic). Drinking some water prior to the dive's good, but too much is as bad as too little. Avoid all those foul-tasting branded sugar water concoctions with added chemicals; water's good and pure.