You'll probably get conflicting advice here, so in the end you'll have to find your own solution.
Does N Wales get hot in mid April? Personally I wouldn't carry water for a medium distance race of 10.5 miles. When I do carry it on longer events, I have a bottle on a waist belt, but only half fill it,as I hate the thing bouncing around. Try different methods on ten mile training runs.
Just adjusting my old fart flat cap
This business of carrying water, energy drinks, energy bars, energy gels is a fairly recent fashion (or clever marketing). The older mob might have considered carrying a handful of raisins on longer distances and drink from a beck. Now I've heard people discussing where best to take their energy gel on a ten mile race in Wiltshire.