The secondary drinking water standards or secondary maximum contaminant levels (SMCL) were established as guidelines by the EPA (but not enforced by the EPA); If they are enforced, they are regulated by each respective state or state health department.
The secondary standards were set because of potential Aesthetic and/or Cosmetic nuisances with the water, or Technical problems with the use of the water and not primarily because of a specific acute or chronic health issue or concern. This should not be interpreted to mean there are no health issues or concerns, but that the contaminant would present an Aesthetic, Cosmetic, or Technical Effect before a significant health risk was apparent. Secondary issues related to the water quality are taste, odor, appearance, or use.
The secondary drinking water standards can be divided into three broad categories:
Aesthetic Effects - undesirable tastes or odors
Cosmetic Effects - effects which do not damage the body but are undesirable, such as skin and tooth discoloration, dingy laundry, and stains/coatings
Technical Effects - effects which can damage or reduce the efficiency of water treatment equipment, household appliances, boilers, heat exchange units, or on-demand water heaters
Even though it is not mentioned, the color and odor of the water are critical secondary drinking water parameters, but these are the effects of problems caused by something else.
We are going to learn about that "something else" and how to build a connection to the Aesthetic, Cosmetic, and Technical Effects problems with your water.
For example, a water which slightly exceeds the secondary drinking water standard for iron might be safe to drink, but the water may have a metallic taste, leave a reddish, yellow-brown, or brown stain on fixtures and laundry, and deposit a discolored coating in piping and fixtures which can impede the water flow. Therefore, this condition caused an Aesthetic problem and has a Technical effect.
Thousands of contaminants might be present in your drinking water, and in most cases it is normally not cost-effective to test for every possible contaminant. However, there are some simple, inexpensive, and visual or Aesthetic clues that can act as "red flags" for possible contamination or an undesirable change in your drinking water quality.
With respect to changes in the Aesthetic quality of the water, the human body has a set of sensors, i.e., the eyes, nose, and mouth, that are great detectors and indicators of change. In evaluating your drinking water, your observations are critical. To aid in using those sensors, we've developed the KnowYourH2O Self-Test Web App that can help you do a preliminary diagnosis of your water.
Below is a link to a table of the Secondary Drinking Water Standards that have been set as guidelines by the EPA as part of establishing National Secondary Drinking Water Regulations (NSDWR) to address issues associated with aesthetic, cosmetic, or technical effects. These guidelines can be considered standards if your state has established specific regulations requiring public water supplies to meet these Secondary Contaminant Levels. (Source)
Also included in the table are the KnowYourH2O (KYH2O) Standards. As part of our Drinking Water Quality Index Calculator, we have developed custom water quality benchmarks to act as quasi standards in order to be able to compare water quality throughout the USA and the world.
KYH2O USA - This is our recommended quasi drinking water standard based on a review of regulations from the U.S EPA, other U.S States, and the Bottled Water Industry.
KYH20 World - This is our recommended quasi drinking water standard based on a review of regulations from the U.S EPA, other U.S States, the Bottled Water Industry, the World Health Organization (WHO), and other nations.