With respect to drinking water, the conditions of the water related to either the presence of individual or a collection of water quality factors that can result in the water having an adverse aesthetic, functional, or economic impact on the quality of the drinking water. It can also have an impact on water related infrastructure, and result in an increased cost to ensure the drinking water is safe for the community and your family. With exception of contaminants that pose a "Health Concern or Condition" the conditions we are discussing are typically related to individual water quality parameters or a combination of parameters that can be as a Secondary Drinking Water Standard and also as an unregulated contaminant with No Standard.
There are a number of water quality parameters that have no regulatory limit that can impact the condition of your drinking water. For example, methane - there is no fixed drinking water standard set by the EPA, but there are some guidance levels. If the methane level of the water is high, the gasses may cause nuisance issues such as "knocking in the piping", "spurting water", low oxidation-reduction potentials that are associated with corrosion. The gas emitted could be flammable or in a confined space be an asphyxiation hazard. "An asphyxiant gas is a nontoxic or minimally toxic gas which reduces or displaces the normal oxygen concentration in breathing air. Breathing of oxygen-depleted air can lead to death by asphyxiation (suffocation). Because many asphyxiant gases are relatively inert and odorless, their presence in high concentration may not be noticed, except in the case of carbon dioxide (hypercapnia)." (Source Wikipedia)