What are three cations and three anions that are commonly found in ground water. Suggest a source for each

Here's a good website:
How Minerals Affect the Water Supplies (http://www.health.state.nd.us/wq/gw/pubs/mineral.htm)

It states lots of impurites and where they might come from. You'll have to do a little work (oh dear) to work out the anions and cations. But I don't believe it's anything very difficult, certainly wouldn't take me 2 seconds.