Question

which ray is used for water purification

Answer 1

.The Environmental Protection Agency recommends reverse osmosis watertreatment to remove radioactive isotopes that emit beta-particle radiation. But iodine-131, a beta emitter, is typically present in water as a dissolved gas, and reverse osmosis is known to be ineffective at capturing gases.

Answer 2

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Purifying is not right word to use here. Purify means removing impurities. Presence of bateria shows contamination.

Ultraviolet ray is normally used to kill the bacteria if present in the water. Sometimes water if contaminated with sewage water may have coliforms such as e-coli and f-coli which are harmful to our health or any virus in water.