I have fairly hard water, and proraso and KMF cream both work fantastic. It just means you will need to work on your lather a bit more.
As for the brush, I do hear of guys doing an apple cider vinegar rinse on their brushes, I don't do such a thing though. You will notice more soap scum build up on your razor (and likely brush) using Proraso and hard water, I sure do!
Hard water will mean that you need to use more soap to get a good lather. Soap will not rinse away as completely as it will with soft water. This means that you will need to clean your gear more often. Soap residue building up in the brush can damage the hairs causing them to fall out. It's a good idea to clean your brush every few months in a mild bath of diluted vinegar and hot water to remove the soap scum build up. A solution of 1 part vinegar and 9 parts hot water should suffice. You only need to soak the brush a few minutes to clean the brush.
Hard water is a pain in the neck. Use a lot of product to produce your lather, and start with as dry a brush as you can. Also, you may try and soak your brush in distilled water. I would not worry, there are soaps that do very well in hard water:
Cella [brick], Institute Karite, TFS (Tcheon Fung Sing) and their BDF offshoot from Bullgoose; various Razorocks and Mitchell's Wool Fat. Assuming you started wet shaving in Sept 2013, it will be time to graduate from creams to soaps around Christmas.