As some people have experienced I am very opinionated on the issue of Creo non-ritual magic. 
I think that there are many arguments against allowing based on magic theory, game balance and the integrity of the setting, so in short I am against allowing non-ritual food or water to nourish.
The arguments pro and con have been discussed very thorougly on the forum and instead of repeating it all I will link to the thread covering the discussion to its fullest. It primarily discussed food, but water is also addresses, but in any regard I would say that they are the same.
I would advice anyone with interest in this field to have a look at it as many people have given their view on it from various positions. If there's any comments after having read the thread I would love to discuss it further. 
As a sidenote I'll add that contrary to my strong opinion against non-ritual nourishment or hydration, I am actually in favour of allowing non-ritual air to sustain you. This is because it is not toppling the setting -you can't sell, trade or monopolize air- and because there is evidence to suggest that medieval thinkers didn't conceive air as supplying anything to the body (as modern science do with oxygen), but rather breathing as something that allowed the body to pass excess bodyheat and to keep the four humours balanced. In other words that the operative need of breathing is the exhalation.