Hydration, Without The Mythology

The familiar two-litres-a-day figure is repeated as a rule but was never meant as one — it traces back to an old intake estimate that included the water already present in food, which is roughly a fifth of most people's total. Actual needs vary enormously with bodyweight, temperature, how much you sweat and what you are doing.

For practical purposes: drink to thirst, have something to hand during a session, and use the colour of your urine as a rough gauge — pale straw is about right, and darker than that usually just means you are behind. One thing that breaks the gauge: B vitamins, riboflavin especially, turn urine a vivid yellow that has nothing to do with hydration, so if you take a multivitamin or a pre-workout the colour will tell you very little for a few hours. Being mildly under-hydrated makes hard training feel harder; it is one of the cheapest things to get right.

One exception worth knowing, because it is the one case where drinking more is the wrong response. If urine is dark brown or cola-coloured rather than simply concentrated, and especially if it follows an unusually hard or unfamiliar session and comes with severe muscle pain, swelling or weakness, that is a reason to seek medical attention the same day rather than to drink more water. It is uncommon, but lifters are one of the groups it happens to, and it is not something to wait out.

Electrolyte drinks are useful in genuinely high-sweat situations — long sessions, hot rooms, heavy sweaters. For a 45-minute session in a British gym, water is almost always sufficient, and whatever you will actually remember to bring beats the ideal drink left at home.