Following on from How can I remove calcium deposits from a drain it looks like my water softener may not be working. How do I measure how hard my water is?
Home improvement stores typically carry test kits. I've found them right by water filters and water softeners. They usually are small paper strips that change color based on levels of hardness. The kit will also come with a legend to allow you to compare the strips.
Conductivity meters may be found online for about $12 American. They'll give you a direct reading in PPM. Some hardware stores carry the things too, but they'll ask $30 plus for them. I tested my cheap one against known standards, and it works just fine.