Annually residences with private wells should have their water tested for bacteria by a state certified laboratory. Typically the water will be tested for Total Coliform Bacteria. Although this bacteria is not considered dangerous its presence indicates the overall bacterial safety of a water supply. The EPA Maximum Contaminant Level (MCL) for coliform bacteria in drinking water is zero (or no) total coliform per 100 ml of water. Typical remediation would require well sanitization. This is a process of injecting chlorine into the well. This will kill the bacteria at least temporarily. In some instances further lab testing will indicate re-occurring coliform bacteria presence after the well sanitization process. In these instances other types of treatment will be required. The most common approaches are chemical injection (typically chlorine bleach) and ultraviolet disinfection. The treatment required will be predicated on the water chemistry. These treatment systems cost between $650.00 and $1000.00.