If you want to determine how much water you need to drink when running you can take a sweat test. It’s easy because you don’t need to see a pro to do it for you.
Weigh yourself naked before and after a 60-minute run. The amount of weight you lose equals how much fluid you typically need per hour. (half a kilogram equals 50oml of fluid)
If you drank during the run subtract that amount from your hourly sweat rate.