Hello Sir, As manufacturer ...

Hello Sir,

As manufacturer of RO, we use only SS316L in drinking water with low TDS (duplex required for high chloride content, which is not the case after RO). Normally, the RO is producing continuously, then no risk of stagnant water. The storage of demi water should be large enough (let's say 1 hour storage to avoid RO starts/stops too often consuming a lot of water for the flush and conductivity control). Microbio should be followed but as any part of the plant and especially at sterilization step before RO. If the design allows CIP operation, everything will be fine. 

Best regards,

Olivier.