Reverse Osmosis Water Filter Systems are the least expensive types of residential water filtration systems. However, most water filtration experts say that these water filters are not the best choice for homes with substantial contamination issues. They mostly only affect color, taste and odors and lack the filtration of contaminants such as bacteria, molds, viruses, etc. To really be on the safe side, one should consider the combination of Activated Carbon Filters with KDF process media since they are the safest and technically most advanced choice in producing clean, pure and contaminant free drinking water.