The pale check

The pair and the glass first need no counting. They do need one check, and it's the one the NHS uses. Once a day, look at the colour of your pee.

What to look for. The NHS says most people should aim to drink enough during the day so that their pee is a clear pale yellow. Dark yellow, strong-smelling pee is on the NHS list of signs of dehydration. Pale, and you're fine. Dark, and you need more, that day, not in general.

When. Not first thing in the morning, which is dark for everyone because you've been asleep for seven hours. Mid-afternoon is the useful one, because it tells you about the working day, which is where the dry day happens. If it's dark at three, that's the flat hour telling you what it is.

What it means. Perrier and colleagues' pooled analysis found that lightening 24-hour pee colour by two shades on the standard eight-point chart went with roughly a litre a day more fluid. You don't need the chart. Pale or not pale is enough. But it tells you that the colour moves with what you drink, quickly, which makes it an honest gauge of the day you've just had.

What it isn't. It's not a diagnosis. Some vitamins and some foods colour pee, some medicines do, and if it's dark and you're drinking well, or it's a colour that isn't yellow at all, that's a GP question and not a water one. And if it's dark and you're also unusually tired or dizzy on standing, that's the urgent list in chapter 20, not this chapter.

The habit. The pale check is ten seconds and it replaces every app, log and bottle marking. It also removes the question "am I drinking enough" from your head, because the answer is in the bowl, and you can look, and then stop thinking about it.

I'd add one thing. For the first fortnight, do the check every afternoon and write down pale or dark, next to the count from chapter 1. That's your evidence, and it will be more convincing than anything in this book, because it's about you.