We live on a semi-rural block & our water is all collected and stored in a rainwater tank. Its lovely and fresh and tases great

We've been in this house about 18mths, we built, so it was brand new & have had the water tested for drinkability etc....all good.
However, the last few times Ive had my colour done (Im not a natural blonde Im afraid

) my hair has done some wierd things. It 'grabs' like buggery around the hairline, and turns grey/blue-ish.....and the roots, dont seem to absorb the tint very well & apears brassy. Within a couple of washes, the grey/blue eases, but my hair is just not quite right anymore.
My hairdresser asked about our water, and recently I had noticed a lime/calcium build up when cleaning the shower, which required full-strength CLR to remove. It was back within a week

Im going to get a sample tested, taken from running hot/warm water (As I understand hard water is more likely to occur when water is heated) and see if this is definately whats happening.
So.....any ideas? Im going to try the Nutrogena hair-cleanser and use camping water for a week. Plus also read it might be worth trying some oils....so perhaps try treating with baby-oil once Ive got rid of the build-up. Has anyone had this problem and found a wonder cure? For my hair & prevention....is there some kind of filter that can soften the water on my shower head?
Thanks, sorry for the tricky one!