Plan fluid around weather, duration, access and personal response rather than copying one rigid target.
Needs change
Heat, humidity, pace, body size, clothing and individual sweat rate affect fluid needs. Start everyday runs normally hydrated and arrange access to drinks when duration or conditions demand it.
Thirst, the forecast and previous experience are useful inputs; no single amount fits everyone.
Practise your plan
Test bottles, packs and event drinks in training. Avoid forcing excessive water, and remember that longer sweaty efforts may require consideration of food or electrolytes.
People with kidney, heart or sodium-related conditions need personalised medical advice.
Know heat warning signs
Stop in a cool place and seek help for dizziness, weakness, nausea, confusion or fainting. Severe confusion or collapse is an emergency.