I often find that healthy portion sizes of fruit and vegetables won't provide us with all the fluid we need but they're a great source of "time-released" fluid. Unlike a glass of water, which leaves the stomach and gets into the blood stream relatively quickly, food takes longer to be digested and therefore releases water into your system more slowly.
The vast majority of deaths during heatwaves are among the eldery and other 'at-risk' groups, which includes the very young and people with pre-existing medical conditions. Some medications can make your skin especially sensitive to sunlight or reduce your body's ability to regulate its own body heat.
Two days of incubation in a child's body is enough for the virus to do its work. If they are unable to fight it they will end up so severely dehydrated they will have to go to hospital, they could end up on a drip, of several weeks, at which point the child's brain and development will have been so severely affected, and in some cases unfortunate enough to lose their life.