What the dry day costs

Put the pieces together and look at the bill. Not because you don't know it, but because it's paid in small amounts across the day and the total never gets added up.

There's the headache at three. Armstrong and Ganio's studies list headache among the symptoms that mild dehydration produced in the laboratory. Yours may have another cause, but if it arrives most afternoons and you've drunk nothing since ten, it's worth suspecting the obvious one.

There's the flat hour itself. Tiredness, low vigour, tasks feeling harder, concentration feeling harder. In the studies those were the clearest effects, clearer than any effect on thinking. That's an hour or two of every working day spent heavier than it needs to be, which over a year is a great deal of afternoon.

There's the stand-in, which is the next chapter, but the bill goes here. A third coffee at three brings caffeine into the evening. The earlier book about coffee covers what that does to the night, and the earlier book about the biscuit tin covers what the four o'clock biscuit does to the six o'clock one. The dry day feeds both habits, because both are answers to a state the dry day creates.

There's mood. Both laboratory studies found mood worse under mild dehydration, and one found tension and anxiety rose at rest. I'd be cautious about the size of that in real life. But a low, slightly irritable afternoon that's partly self-supplied is a cost to the people around you as well as to you.

And there's the night. If the first proper drink of the day is a glass of wine at six, or a large glass of water at ten because you suddenly feel it, you get the visits at night that chapter 10 was trying to spare you. The dry day pushes drinking to the end of the day and then charges you for it at two in the morning.

None of these is large on its own. That's the point. A day of them is nothing, and a decade of them is your afternoons.