# The Water Supply (Water Fittings) Regulations 1999, Paragraph 20


(1) No vent pipe from a primary circuit shall determine over a storage cistern containing wholesome water for domestic supply or for supplying water to a secondary system.
(2) No vent pipe from a secondary circuit shall terminate over any combined feed and expansion cistern connection to a primary circuit.

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Source: https://www.legislation.gov.uk/uksi/1999/1148/schedule/2/paragraph/20 (the official version)
Page: https://openlegislation.uk/water-supply-water-fittings-regulations-1999/schedule-2/paragraph-20
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.