You may have more than one water profile with the same name. BeerSmith indexes all profiles from only the name field. You'll need to either delete the old versions or rename them.
As an aside. If you're seeking greater accuracy, getting a water sample analysis about every 3 months will help you refine your water more accurately. Water quality reports are composite averages over their entire district, for a year. Various places within a district may have different sources and ratios from others. The report may encompass sources that are transient to your location, or not used at all.