The World Health Organization (WHO) and the Department of Health advise that water suppliers insist on separating the drinking water tap from the softened water taps and pipes in the premises.
The Water Quality Regulations 2000 require a maximum limit of 200 milligrams per litre for sodium in drinking water. This limit should not be exceeded for infant food preparation and for people on low-sodium diet.
The Regulations also state that "All premises supplied with water for domestic purposes shall have at least one tap conveniently situated for the drawing of drinking water".
With ion exchange softened water, the 200 mg/l limit is very hard to keep in the areas of extremely hard water, such as South-East England and London.
Therefore, it is very important that installers ask the local water supplier about the level of water hardness and sodium in the area, and advise clients accordingly, so that the sodium level after softening does not exceed 200 mg/l.