Hydration is the most underrated performance variable in most recreational athletes' training. Dehydration of just 1-2% of body weight measurably impairs strength output, endurance, reaction time, and cognitive function. Yet many athletes train regularly in a mildly dehydrated state, accepting suboptimal performance as normal when the solution is simply drinking more water.
Baseline hydration needs: 35-40ml per kilogram of body weight per day for physically active adults. For an 80kg athlete, that's 2.8-3.2 litres daily without accounting for exercise. Add 500-1000ml per hour of moderate-intensity exercise, more in hot conditions. In Australian summer heat during outdoor training, fluid losses of 1-2 litres per hour are common and must be replaced during and after activity.
Urine colour is the simplest hydration marker: pale yellow indicates good hydration, dark yellow indicates dehydration, and colourless indicates over-hydration (which, while less concerning than dehydration, dilutes electrolytes). Weigh yourself before and after training - each kilogram of weight lost represents approximately 1 litre of fluid deficit. Re-hydrate with 1.5 times the fluid lost (500ml per 500g of weight loss, totalling 750ml). Pre-training hydration: drink 500ml of water 2 hours before training to ensure adequate hydration without discomfort. During training exceeding 60 minutes: 150-250ml every 15-20 minutes. Electrolytes (sodium, potassium, magnesium) are needed in sessions exceeding 90 minutes, particularly in hot conditions.