Parah 6:4-5

Parah 6:4

If one put his hand or foot or some vegetable leaves so that water would flow into a jar (to be mixed with the ashes), the water is unfit (because it came into the jar via something that is susceptible to ritual impurity). If he used leaves from reeds or nuts, then the water remains fit. The general rule is that water that passes over something susceptible to impurity is unfit, while water that passes over something insusceptible to impurity remains fit.

Parah 6:5

If someone diverted a spring into a vat or cisterns, the water is unfit for a zav or a metzora’s purification, or for the sanctification water. This is because it wasn’t collected in a vessel.