How can i tell whether or not an aquatic snail is dead?

because of the weather, the water is lowering at a local lake... i found a large aquatic snail on the lake shore... it has its protective covering over the opening of the shell... ..... ..... .... i brought the guy home thinking i'd see it peek out and re fill its water supply, but that has yet to happen. its been sitting in a bowl of water for 4 or 5 hours now, not doing anything. how do i know if its alive?|||While I agree it probably wasn't in the snails best interest to take it from it's natural home, if it has a "trap door" look, where it can totally put its body in the shell and close a "door". If you touch the snail and the door is tightly closed, its alive, if you touch it and the door hangs slightly open it's dead.|||If the water is from the tap and not the lake, then you probably have come close to killing it. You need to dechlorinate the water or the snail will die. You don't know how to take care of this animal so you never should have taken it in the first place.|||ya should have threw it back in the lave if u didn't no how 2 take care of it!!