Article R1321-57 of the French Public Health Code
The internal networks mentioned in 3° of article R. 1321-43 may not, unless the Prefect grants an exemption, be supplied with water from a resource that has not been authorised in application of article L. 1321-7. They must not, as a result of the conditions in which they are used, particularly in the event of backflow, be able to disrupt the operation of the network to which they are connected…