For purification

Limestone is composed mainly of calcium carbonate (CaCO3), which can act as a natural filter. As water passes over and through limestone, the calcium carbonate can neutralize acidity in the water, which is particularly helpful in areas where acid rain is a problem. Limestone can also precipitate certain impurities, removing them from the water. Additionally, the porous nature of limestone allows it to act like a sponge, absorbing water and filtering out larger particles of dirt and debris. - helped by chatgpt

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