If it were to be implemented, the best way I can imagine is to have a canteen system. Your seraph will automatically drink from your canteen (inventory, maybe a new slot?), and you will have to refill it now and then (making sure to disinfect and/or filter). This adds a challenge in environments with very little freshwater, on long-distance voyages and sailing, and doesn't force you to frequently interact.
In my opinion, this system actually sounds pretty fun to have in the game because it challenges the player and fits into the progression system. Your first canteen could be made of hide, the next one metal, then leather, etc. Charcoal filters would clear up dirt, and boiling the water would disinfect it. Anyone who's sunk their teeth into the game should be able to do this in their first couple of days; However, that's the problem. This could be hard early on and very frustrating for first-time players, which is why I suspect this system isn't in the game despite the rigor of Vintage Story's survival mechanics.