"I don't like the taste"

Some people don't, and it's not an affectation. Water from a tap in a hard-water area has a taste, water from a plastic bottle that's been on a desk all day has a different one, and if you grew up drinking squash, plain water can seem like a punishment. The belief that follows is that drinking more fluid means drinking more of a thing you don't like, so it won't last.

It doesn't have to be water. This is the NHS's position and I'd repeat it as often as needed. Tea and coffee count, sugar-free drinks count, lower-fat milk counts, and the NHS suggests sparkling water, no-added-sugar squash, or a slice of lemon or lime if you don't like the taste of plain water. The fluid is the point. The water is just the cheapest way to get it.

So the pair in chapter 16 can be a mug of tea next to the coffee, if that's what you'll drink. It can be a glass of diluted squash with lunch. It can be sparkling water, which some people who dislike still water find fine. The rule is a glass of something without sugar in it, alongside things you already do, and taste is allowed to decide what's in the glass.

There are two limits. Sugary drinks and fruit juice do count as fluid, but the NHS says to limit juice and smoothies to one small glass a day with a meal, and not to have drinks high in sugar too often, because of teeth and calories. A day of cola is hydrated and paying for it elsewhere. And an all-tea approach runs into the caffeine question in the evening, which an earlier book, You were tired at ten, covers, and which chapter 12 touches on.

The honest objection is that even squash gets dull. What I'd say to that is that dull is the point. The drink in the pair isn't meant to be looked forward to. It's meant to be there, next to the thing you do look forward to, and drunk without ceremony. Dullness in a drink is a feature when the drink's job is to be had six times a day.