Provided is a reverse osmosis membrane treatment method by which scale failure can be avoided in a condition where water to be treated is neutral to alkaline. A chelating agent is intermittently added to the water to be treated on which a reverse osmosis treatment is performed, or the chelating agent is consecutively added to the water to be treated and the addition amount is intermittently increased. At this time, the pH of the water to be treated is at least seven, and more preferably, the pH of the water to be treated is at least nine. If necessary, a scale inhibitor can be added to the water to be treated along with the chelating agent.
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