I have soft grainy brown stuff coming out of my cold water faucets and toilets.

If you are on a well it's likely that it's iron deposits (may be same if on municipal water system too). Water may be yellow brownish in colour with visible particles (especially if you let a pail of the water sit for a while). A simple carbon filter system (purchased from a hardware or plumbing store) can easily and cheaply remove this (and other stuff) from your water. Likely not a serious health risk just an aesthetic one. If really worried about your water quality it can be tested by getting sample kits from possibly your local hospital, Dr. office, Public Works. Depends on where you live and how that area does testing for the public. A plumber would also know about how to get testing done (might be a good idea from time to time anyway if on a well). If on a municipal system they may have been flushing out the water mains in the roads in your area which can cause this too.