I'm a water treatment engineer. Carbon filtration will remove dissolved solids and heavy metals, and with high efficiency if done correctly. Most GAC columns designed to remove lead and heavy metals are enriched with sulfide ions to increase the removal efficiency as well. People prefer to use ion exchange resins to remove heavy metals because they can be regenerated more easily and efficiently. Also ion exchange resins allow you to recover any absorbed minerals.
Carbon filtration doesn't remove fluoride, does it? (Or arsenic) The only water filtration system I have found that removes fluoride is the Berkey brand. I've not seen any filtration systems in the stores even mentioning fluoride or arsenic.
This is totally correct. It is also not very applicable to drinking water & whole house systems that homeowners are interested in.
There are carbon cartridges with ion-exchanges resins blended into the block that seem to be effective for lead removal at low flow rates. They tend to have lower flow-rates and capacity than is ideal.
http://ascelibrary.org/doi/10.1061/%28ASCE%290733-9372%28199...