Apparently yes [1]: > Until 1 January 2001, the use of siphon-type cisterns was mandatory in the UK[12] to avoid the potential waste of water by millions of le

Apparently yes [1]: > Until 1 January 2001, the use of siphon-type cisterns was mandatory in the UK[12] to avoid the potential waste of water by millions of leaking toilets with flapper valves, but due to EU harmonisation the regulations have changed. [1] https://en.m.wikipedia.org/wiki/Flush_toilet#Siphon-flush_mechanism https://en.m.wikipedia.org/wiki/Flush_toilet#Siphon-flush_me...