i live in a hard water area and dont have a softener. however, in an ideal situation you should do. it will prolong the life of the RO filters as they do not have as much work to do.
on saying this, i always give my customers the option of having a softener with their filters, and the majority choose against it. up to now there hasnt been any problems with people not running them (some have been in hard water areas with a ppm of 600!!!
)
however, my advice would be if you have the money to buy/run one and dont mind the "hassle" of changing salt tablets and regenerating one then go for it.
you can get a manual softener kit for about £150ish , or an electric one from £250ish upwards.
WELMAC - Gary