Parah 11:1

If one left a flask of sanctification water uncovered but when he returned he found it covered, it’s invalidated. If he left it covered and returned to find it uncovered, it’s invalid if a weasel could have drunk from it – or a snake according to Rabban Gamaliel – or if dew fell into it overnight. Sanctification water is not protected by a tight-fitting cover but water that has not yet been sanctified is.

Parah 11:2

Any case of doubt that is ruled ritually clean regarding trumah is also considered clean vis-à-vis sanctification water. Anything that is suspended (i.e., neither eaten nor burned) when it comes to trumah is spilled out when it comes to sanctification water. If a person was sprinkled with such water and he handled ritually-clean things, those things are suspended. A lattice of wood is ritually clean vis-à-vis sanctified food, trumah and sanctification water; Rabbi Eliezer says that loosely-connected wood is unclean vis-à-vis sanctification water.