The absence of a red heifer is a major argument against rebuilding the Temple, and the major one against ascending the Temple Mount. Unable to purify themselves with red heifer ashes, Jews remain in a perpetual state of ritual impurity from corpse contamination.
The impurity, however, might not be perpetual. Formulations such as “he will be unclean until evening” and “for seven days” suggest that the state of impurity is finite.
Numbers 19:17 prescribes taking ashes for each purification. It is not possible, therefore, that the Temple priests diluted the ashes of a single ultra-rare cow to homeopathic proportions and distributed the resulting water. No, ashes had to be readily available in every village if we’re to take seriously the v.20 curse: everyone who is not purified should be banished.
Originally, Numbers 19 dealt only with the impurity of touching a corpse. Later, under-the-roof impurities were added in v.v.14–18. The expansion could only have been possible with a ready supply of red heifer ashes in many locations. That is probable, as v.2 merely demands that the cow be without blemish (“total”), which hardly substantiates the rabbinical demand that every hair on it be red, with the exception of two hairs at most. At the very least, the owner of a prospective red heifer would carefully pluck the non-red hairs before offering it for sale to the Temple.
Any red cow will do.