Why does the account of Miriam’s death follow the [laws of the] red heifer? To teach us you that even as the red heifer achieves atonement, so does the death of the righteous achieve atonement.
(Talmud, Mo’ed Kattan 28a)
Three great providers arose for the people of Israel–Moses, Aaron and Miriam–through whom they received three great gifts: the well, the clouds [of glory], and the manna. The well was in the merit of Miriam, the clouds in the merit of Aaron, and the manna in the merit of Moses.
When Miriam died, the well was removed, as it says, "And Miriam died there…" and, immediately afterward, "And there was no water for the congregation." The well then resumed in the merit of the other two.
When Aaron died, the clouds of glory were removed, as it says, "And the Canaanite, the King of Arad, heard …and waged war on Israel." He heard that Aaron died, and thought that he now had license to attack Israel [because the clouds of glory which protected them were gone. The well and the clouds] then resumed in the merit of Moses alone.
(Talmud, Taanit 9a)
A people have various needs, and different types of leaders arise to provide them. Spiritually, too, a nation requires "food," "air" and "water" — wisdom, faith and guidance. Again, different leaders arise to provide these different needs, each according to his or her specialty.
But there may come a time when a leader cannot afford the luxury of "specialization." He may be capable of teaching Torah on the highest level, but there is no one to teach the children alef-bet. He may be suited to raise the most spiritual souls to sublime heights, but there is no one to sustain the simple faith of the common man or to provide guidance on the most commonplace dilemmas of life. In such times, the true leader assumes all these tasks, as Moses did in the closing days of Israel’s sojourn in the desert, when the people stood at the threshold of the Promised Land. Miriam and Aaron were no more, and Moses served as shepherd, nurse and guardian of faith in one.
(The Lubavitcher Rebbe)
A person may ingest the ingredients of life, but these will not vitalize him without the fluids that course through his body. The food swallowed by the stomach, the oxygen drawn in by the lungs, must now be transported through the body’s canals and made to saturate its every cell.
Therein lies the spiritual significance of Miriam’s role as Israel’s provider of "water." Miriam first appears in the Torah (see Midrashim and commentaries on Exodus 1:15) as a children’s nurse: one who distills adult food for the consumption of a child; one who trains and educates a growing human being, filtering the stimuli of an adult world for his maturing mind; who processes the raw materials of life to meet the specific needs of her charge’s age and phase of development.
Miriam’s well is the vital fluid of Israel’s spiritual life, the water that inculcates them with the knowledge and identity her brothers provide. The waters of Miriam transport and apply the nutrients of Torah and the abstractions of faith to each individual, on his or her particular level.