Why an exercise scientist says 'drink more water' is the wrong advice.

The advice on every water bottle: drink two to three litres and you are sorted. The physiology says otherwise. Fluid only stays where you need it if sodium and potassium pull it into your cells and hold it there. Without them you drink, you pee, and you are thirsty again inside the hour. That is why the three-litres-a-day crowd still feel flat at 3pm.

Thirst is a lagging indicator. Reaction time, focus and mood slip first, quietly, while you are still telling yourself you are fine. The email you read three times at 2pm. The short fuse at 4pm. Most people put that down to willpower or a bad night. It is usually fluid, and the second coffee pulls in the wrong direction.

Two percent of body weight in sweat is where the research starts to see performance and mood drop off. For a 70kg person that is 1.4 litres. A hot commute plus a gym session gets you there. So does a day outside with the kids, or an air-conditioned office and three coffees. Most Australians hit it most days and never connect it to how they feel. Dr Kendall's rule of thumb: at 2% your core temperature climbs and it starts affecting you mentally before it shows up physically.

The industry trick is simple: add just enough sodium to print the word electrolytes on the front, usually 100 to 200mg, less than a slice of bread, then fill the rest with 30g of sugar and a sports sponsorship. Hyro is dosed at the levels the studies actually use: 500mg sodium, 250mg potassium, 100mg magnesium, and 0.03g of sugar per stick. The numbers are on the pack. Compare them to whatever is in your cupboard.

After a hard session, a 35 degree day or a big night, the first thing your body is short of is not calories. It is the water and salt you sweated out, and a protein shake does nothing about that. Put the fluid and electrolytes back in and the next morning stops hurting: fewer cramps, less heaviness in the legs, and you actually feel like moving again.

It is not a pre-workout. You will not feel it in ten minutes, and it will not undo five hours of sleep. What it does is quieter and more useful: one 4g stick in your first bottle of water, every day. Most people notice the afternoon slump fading by week two and the heavy mornings gone by week four. If you do not, the 30-day guarantee means you do not pay. It lands on your doorstep every 30 or 60 days, and you can skip, pause, swap flavours or cancel any time.