If two protective filters are arranged in parallel, it is essential to ensure that they are operated simultaneously and that there is a constant flow through them. This is mainly for hygienic reasons: The main thing is to avoid stagnation.
For the same reason, there must be no bypass lines in the installation. In addition to hygiene problems caused by stagnant water, there is also the risk of dirt particles being flushed in. The regulations for this can be found in german DIN 1988-200, 12.4.3. and german VDI/DVGW 6023.