When I watched my house foundations being poured onto clean white chalk, and a 12th century church just up the road is built with "clunch" blocks and flints, and any digging in the garden results in me often throwing chunks into the hedge; it is difficult to think of actually adding it to anything I grow in. Tap water here is similarly "hard". 99% of the water I use in my greenhouse is collected rain water (and pots in the garden when I have enough) so maybe I should think about Ca levels sometimes, although I use bonemeal a lot so never short of Ca.