The castor should be pretty safe as the heat destroys the toxin in the raw seed.

Try a simple carbon and sediment filter . Think that will be pretty standard. So unless you're in a high farming community or cattle that may taint the ground water - should be good. You can take a sample unfiltered and have it tested for bacteria etc. If there is any, the community should address that as a whole.

Good luck in the shift . I'd still use a carbon and sediment filter on city water. :)