Water Stains on unsealed granite

We have Ubatuba granite for our kitchen countertops.  It was installed 5 years ago and the installer did not seal it, just polished it.  Over the last few years, we've gotten white stains (hard water, I think) around the faucet.  How can these be removed, if at all?  Do we need to have the granite sealed now?  We also have a problem with drinks leaving a dark ring for a while after it dries.  Would sealing the granite fix this?  We use soap and water to clean it, is this right?  Thanks in advance for any advice!