Storing - How long does methamphetamine stay stable in solution?

[sknkv2]

SWIM's hamburger is planning on taking some meth tonight but isn't going to be at a place where he can readily take it out to consume it, so he plans on dissolving it in a bottle of water and drinking the desired amount. SWIM is just wondering since he may not finish the bottle, how long will it stay good for? He can't keep it in the fridge/freezer as it may be mistaken as water by other members of the household so yeh, at normal temperature how long can swim's hamburger expect it to stay good for?

P.S. Swim quickly searched but couldn't find anything, so if it's been covered link would be handy.