Systematic

The more I look at this situation, it looks like we need to:

1. Determine what contaminates will be getting into rain water as a result of volcanic activity and possibly earthquakes. This could be done by researching studies done on existing volcanoes and eruptions and what they cause.
2. Estimate levels (or range of level i.e. + or -) of hazardous contaminants that needs to be filtered. Done mostly from studies on existing volcanic activity.
3. Determine what contaminants are most harmful that will need to be filtered.
4. Investigate - research each filter type to determine what amount it will filter out for each of the hazardous contaminants.
5. Then, recommend the chosen filter technologies - companies.

In this way we can get workability and practical solutions.

Offered by Mike.