On Mar 17, 11:19*am, "GB" wrote:
I need a very small water softener to produce a few litres of soft water a
day - for a humidifier.

Get a commercial water filter housing and a water softener filter
cartridge. You could probably regenerate the cartridge by running
brine through it and then flushing with clean water.

http://www.fileder.co.uk/brochure/58.htm

Softening doesn't remove the dissolved solids, it makes them much
more soluble. The humidifier should be blown-down or rinsed out
intermittently to reduce the TDS.