If the pipe run from before the water softener to the kitchen sink
is difficult, then the separate hard water supply can be run in 3mm
drinking water line which is very small indeed.
It can be tucked under carpets, behind coving and generally made to
disappear. Due to the low flow rate, an accumulator tank must be
installed under the kitchen sink. These contain 4 litres of hard
water readily available instantly, so you can fill your kettle and
within a few minutes the tank is full again.