"Coffee counts, so I'm fine"

This one is half right, and the half that's right matters, so I'll give it first. The NHS says that water, lower-fat milk and sugar-free drinks, including tea and coffee, all count towards your daily fluid intake. Sophie Killer, Andrew Blannin and Asker Jeukendrup took 50 men who normally drank three to six cups of coffee a day and had them drink either four cups of coffee or the same volume of water each day for three days, with everything else controlled. Total body water didn't differ, and neither did the volume of pee over 24 hours or any of the blood markers. If you drink coffee regularly, a cup of coffee is a cup of fluid.

So the two coffees before eleven are two cups towards the six to eight the NHS mentions. The trouble is what comes after eleven, which in the day in chapter 1 was a can at lunch and a third coffee at three. That's four cups, at most, across a whole working day, most of them before mid-morning. The coffee counts. It just doesn't add up to enough, and it stops early.

There's a second thing, which is what the coffee is for. The ten o'clock coffee isn't reached for because you're thirsty. It's reached for because someone's going to the machine, and because of the lift. The three o'clock one is reached for because of the flat hour. Coffee is being drunk for its effect, and happens to bring fluid with it. An earlier book in this series, The second coffee, is about the effect, and about what a habitual dose does and doesn't give you, and I won't repeat it here. For this book the point is simpler. If you drink coffee for the lift, you'll stop drinking it when the lift stops being wanted, at about eleven, and nothing takes its place.

The honest objection is that some people drink tea all day, six or seven mugs, and for them the count is fine and this chapter doesn't apply. It's worth checking that you're one of them and not one of the people who think they are and had two.

The pair, in chapter 16, doesn't take the coffee away. It puts a glass of water next to it, so that the drinks you already have for their effect bring a second drink with them, and the count carries on past eleven whether you feel like it or not.