As outlined in the General Match Requirements, for Junior U11 and Youth football matches (U12 to U16), each team is required to provide at least one Water Carrier for each game. This person is required to act according to the rules of the game (as outlined below). For most matches 2 Water Carriers are assigned to ensure players are adequately hydrated.
The following information has been taken from the AFLs "Laws of Australian Football 2012"
Each Team Official (Water Carriers) and Team Runner(s) shall wear a uniform or other form of identification (such as a bib or armband), as determined by the Controlling Body.
A person(s) appointed to deliver water to players of a Team during a Match. Water carriers are not permitted to provide instruction to players during a match.
13.5 Official within Fifty-Metre Arc
Unless attending to an injured Player, no Official (including Water Carriers) is permitted within the Fifty-Metre Arc during the time when a defensive Player is preparing to Kick or in the act of Kicking the football back into play after a Behind has been scored. Additionally, Water Carriers are not permitted to deliver water to players in the 50 metre zone where the football is in play, ie: Water can only be provided to players in the remaining two 50 Metre zones where the football is not in play.
Where an Official contravenes this Law, the opposing Team shall be awarded a Free Kick at the back line of the Centre Square, to be taken by the Player from the opposing Team who is closest to that location.
Reference Source: Laws of Australian Football 2012