"I haven't got time to think about it"

The last of the reasonable objections is that hydration is one more thing. There are apps that remind you to drink, bottles with hours marked on the side, and the whole thing has become a small industry of nagging. You've got enough to think about, and adding "have I drunk enough" to the list is a cost in itself.

I agree with all of that, and the method in this book is built to need no thinking. The pair isn't a reminder. It's a glass that stands next to the coffee. When you make the coffee, you pour the glass. When lunch is on the table, the glass is on the table. You don't have to remember anything, because the coffee and the lunch already happen and they carry the glass with them. A habit attached to an existing one doesn't need to be tracked. It needs a fortnight of doing the two things together until the second one stops being a decision.

The apps and the marked bottles fail, I think, for a reason worth naming. They ask you to drink at times chosen by a clock, which have nothing to do with what you're doing, so every reminder arrives as an interruption and gets dismissed. The pair asks you to drink at times chosen by your day, which is when you were already stopping for a drink. Nothing new is scheduled. Something existing is doubled.

There's one piece of thinking left, and it's ten seconds once a day, which is the pale check in chapter 18. That's the whole overhead. No counting, no log, no target in millilitres. A glass with each hot drink and each meal, and a glance at the bowl.

The honest objection is that even the pair needs a glass, and a glass needs finding and filling and carrying, and on a bad day that's enough friction to stop it. Fair. The fix is to leave one glass or one bottle where the coffee gets made and one where you sit, and never put them away. The friction isn't the drinking. It's the fetching, and the fetching can be removed once.