PRODUCTION METHOD OF PURIFIED WATER AND PRODUCTION DEVICE OF PURIFIED WATER

To provide a production method of purified water which can reduce a used amount of a pH adjusting agent while always satisfactorily maintaining the quality of permeated water after treatment with a reverse osmosis membrane.SOLUTION: A production method of purified water comprises: measuring a pH of water to be treated which flows into a decarboxylation device 6, a pH of decarboxylation-treated water which flows into a reverse osmosis membrane 12, and the quality of permeated water which flows out of a reverse osmosis membrane 14 when purified water is produced by treating the water to be treated with the reverse osmosis membranes 12, 14 after decarboxylation treatment; and adjusting the pH of the water to be treated or the pH of the decarboxylation-treated water on the basis of the pHs of the water to be treated and the decarboxylation-treated water and the quality of the permeated water so that the quality of the permeated water satisfies a predetermined water quality range. The pH adjustment includes: rising a pH set range of the water to be treated when the quality of the permeated water satisfies the water quality range; lowering the pH set range of the water to be treated when the quality of the permeated water does not satisfy the water quality range; or adjusting the pH set range of the decarboxylation-treated water when the quality of the permeated water does not satisfy the water quality range although lowering the pH set range of the decarboxylation-treated water in a preceding adjustment time.SELECTED DRAWING: Figure 3 【課題】逆浸透膜による処理後の透過水の水質を常に良好に維持しつつ、ｐＨ調整剤の使用量を低減することが可能な精製水の製造方法を提供する。【解決手段】脱炭酸処理後に、逆浸透膜１２、１４で処理して精製水を製造する際に、脱炭酸装置６に流入する被処理水のｐＨ、逆浸透膜１２に流入する脱炭酸処理水のｐＨ、逆浸透膜１４から流出する透過水の水質を測定し、被処理水及び脱炭酸処理水のｐＨと透過水の水質に基づき、透過水の水質が予め定めた水質範囲を満たすように、被処理水のｐＨまたは脱炭酸処理水のｐＨを調整し、そのｐＨ調整は、透過水の水質が水質範囲を満たす場合に被処理水のｐＨ設定範囲を上昇させ、または透過水の水質が水質範囲を満たさない場合に被処理水のｐＨ設定範囲を下降させ、または先行の調整時期にて脱炭酸処理水のｐＨ設定範囲を低下させても透過水の水質が水質範囲を満たさない場合に、脱炭酸処理水のｐＨ設定範囲を調整する。【選択図】図３