PROBLEM TO BE SOLVED: To carry out hot water washing of an apparatus for producing dilution water for making dialysate, in a comparatively short time to maintain the apparatus at high cleanliness for a long period of time.SOLUTION: The apparatus includes a raw water storage tank 3, a pretreatment means 5 containing activated carbon, an RO membrane module 8, a purified water storage tank 9, etc., arranged in this order. An EDI 15 is installed to separate permeated water from the RO membrane module 8 into desalted water, electrode water and concentrated water. The apparatus further includes a desalted water supply passage 24 for supplying desalted water from the EDI to the purified water storage tank 9； circulating lines 12, 13, 21, 22, 23 for returning the permeated water and concentrated water from the RO film module 8 and the desalted water, electrode water and concentrated water from the EDI 15 to the raw water storage tank 3； a heating means 28 provided at the raw water storage tank 3 to heat raw water in the raw water storage tank 3 and circulating water into the raw water storage tank 3 when the RO membrane module 8 and EDI 15 are washed with hot water； and a three-way valve 25 for switching the desalted water supply passage 24 to the desalted water circulating line 21 so that the desalted water in the desalted water supply passage 24 is not supplied to the purified water storage tank 9 during hot water washing.【課題】透析液作成用希釈水の製造装置にて、比較的短い時間で装置の熱水洗浄を実施して装置を長期間高い清浄度に維持する。【解決手段】原水貯留槽３と、活性炭を含む前処理手段５、ＲＯ膜モジュール８、精製水貯留槽９等がこの順番で配置される。ＲＯ膜モジュール８からの透過水を脱塩水と電極水と濃縮水に分離するＥＤＩ１５が設置される。ＥＤＩの脱塩水を精製水貯留槽９に供給する脱塩水供給路２４と、ＲＯ膜モジュール８の透過水と濃縮水、ならびにＥＤＩ１５の脱塩水と電極水と濃縮水を原水貯留槽３に戻す循環経路１２，１３，２１，２２，２３と、ＲＯ膜モジュール８とＥＤＩ１５の熱湯洗浄時に原水貯留槽３内の原水と原水貯留槽３内への循環水を加温する、原水貯留槽３に付設された加温手段２８と、熱湯洗浄のとき、脱塩水供給路２４の脱塩水が精製水貯留槽９に供給されないように脱塩水供給路２４を脱塩水循環経路２１に切り替える三方弁２５と、が設けられている。【選択図】図１
