I always enjoy reading hundred-year-old advice. Sometimes I agree with it; other times I just smile. Here is what a century-old home economics textbook says about drinking water:
That drinking water at meals is harmful is another tradition to which some people still cling. There may be certain pathological conditions that would make this practice harmful. But people in normal health suffer no ill effects from a reasonable amount of water taken with meals. A safe rule at meals is to drink when you are thirsty, and with one limitation not to drink when masticating.
The digestion of starch foods should begin in the mouth and this can take place only when the food is thoroughly mixed with the saliva. If food is mixed with water the salivary glands are not sufficiently stimulated to action, and the food passes from the mouth without enough of the digestive juice.
One disadvantage of drinking water at meals is that people who do so often think they have a sufficient amount and do not drink between meals. Copious water-drinking is essential for proper elimination. It is a safe rule to take at least six glasses a day, including that taken at meals, and ten glasses are not too much.
How to Cook and Why by Elizabeth Condit and Jessie Long (1914)