High calcium is generally not a detriment to beer flavor. It has little flavor impact. However, the high calcium can drive the RA of the water down. If you start with RO or distilled water, it could be possible to need some alkalinity in the water to help avoid an excessive mash pH drop.
Martin, How is this best accomplished? It has been a while since I even considered RA, as I found myself chasing my tail: add salts to increase RA, add salts to decrease pH, repeat.
I use 100% RO water, and frequently my RA is very low. For example I brewed a Baltic Porter where the RA was -71. Pretty low for a very dark beer (fortunately it tastes great!). I have been just targeting Palmer's recommended ranges while maintaining a good mash pH, but would love to get my head around the concept of RA as it relates to RO water.
BTW, thanks for your comments on this thread. I have copied and pasted them to a Word Doc so I can reference them later.