Its about 50/50 prolly slightly more areas with soft water than hard water areas in UK straight from tap Trex. Its kinda North and South thing again with our water
Here`s a rough map gives you an idea although not totally accurate.

I'm soft water area and i dont use calmag unless im buffering old coco or prepping clayballs. The UK ferts aren`t too bad they kinda tailor them for whatever area your from ie: softwater or hardwater A&B.



