Air gap to drain

An air gap is required by regulation when installing a water softener.  The drain connection discharges waste water to the drain during a recharge only.
The drain connection from the softener can be via a waste pipe upstand but it must incorporate the
regulation air gap of 20mm on the drain (an unobstructed gap between the outlet from the
softener and the drain connection).

Reason,

If there is a blockage or back-pressure in the drain, water from the drain cannot be drawn into the softener.

If you are discharging water into an open drain (such as a gully) this can be used to incorporate your 20mm air gap.

An example of a plumbing connection that can be purchased from any Plumbers merchant if access to the waste pipe is difficult is shown below.