I usually just fly until I overheat, then run a little bit, waiting for cooldown, then takeoff again. I never considered flying near water sources, until I saw an Interceptor do it, in game.
I am planning on playing the Ranger and Storm classes (Javelins) in Anthem, mainly due to time constraints. That is, I will not have the time to focus on more than two Javelins. Plus I do not like tank (Colossus) and melee (Interceptor) classes.
"This Is Anthem" is a gameplay series by BioWare. Part 1 below provides an overview of Anthem's story, progression, Javelins and customization.