Hydration for 5k running or even racing is not that difficult when compared to a Marathon.
If you ever get the chance then look for an Olympic 5000m race. Watch it. Notice they will never take liquids. OK they do finish just a bit before you and I would.
Anyway the point is they are going flat out and pushing their bodies to the limit and they do not need to take on board liquids during the race. The same is true for 10,000m (10k).
So why do you need to take on liquids?
A: You don’t.
Even if you are a beginner, an older competitor, slightly overweight, a child, or whatever, chances are you’ll do 5k in less than 45 minutes in 99% of the cases. You do not need to take on liquids for a 45 minute run.
You might WANT to. That’s fine if it makes you feel comfortable.
It would be prudent to ensure you are always properly hydrated (check the colour of your urine which should be a very pale yellow colour). And ignore the nonsense about needing to drink 2-3 litres of water a day, every day – That was probably sponsored by Evian or Perrier or Thames Water. That is just rubbish – perhaps 1-2 litres on a hot English Summer’s day is enough (but check your wee!).
So assuming you are properly hydrated then 500ml of lucozade sport an hour before a race would be ok for hydration and a similar 500ml of a recovery drink afterwards will sort you out very nicely.
Enjoy the run and don’t worry about the hydration…it’s not a Marathon.