As the London Marathon approaches, runners are focusing on their hydration strategies, especially after temperatures reached 22.2°C (72°F) last April. Proper hydration is key to marathon success, significantly impacting performance. Olympic marathon runner Rose Harvey advises starting hydration early with electrolyte drinks the night before and on race morning. Dr. Sam Shepherd from Precision Fuel & Hydration recommends against generic hydration plans, as individual needs differ based on sweat rate and sodium loss. Common hydration mistakes include overhydration, dehydration, ignoring electrolytes, waiting until thirsty, and inconsistent hydration.