What Happens When You Drink a Gallon of Water a Day?

Water is great but it is much better and safer to base the amount you consume on your weight and activity level rather than a fixed amount such as 1 gallon per day. This is the conclusion the author came to also.

Here is a calculator that might be appropriate. https://goodcalculators.com/water-intake-calculator/

"A switch to water that’s been ultrapurified by reverse osmosis (plus “carbon polishing” and UV sterilization) has proved revelatory."

This can mess with one's electrolyte balance to a dangerous degree. (She makes a vague reference to buying an "electrolyte mix", but that's before switching to purified water, and she makes no mention of using any.)