Colorado’s Primary Drinking Water Regulations (Regulation 11) match EPA’s federal Safe Drinking Water Act in setting both Maximum Contaminant Levels (MCLs) and Secondary Maximum Contaminant Levels (SMCLs). Contaminants with MCLs are often referred to as primary contaminants with primary standards. Contaminants with SMCLs are often referred to as secondary contaminants with secondary standards. Public water systems are required to test for primary contaminants to address situations where primary MCLs are exceeded, ensuring drinking water quality does not exceed any primary contaminant standards. It’s a far different picture for secondary contaminants.
Generally, public water systems are not required to test for secondary contaminants, except for fluoride, which also has a primary MCL. When fluoride levels exceed the SMCL of 2.0 mg/L but not the MCL of 4.0 mg/L, public water systems are required to issue a special public notice due to the risk of dental fluorosis (discoloration and pitting of teeth in children while they are growing under the gums). This is thought to impact the appearance of the teeth but not impact health.
Manganese is also handled a bit differently. There is a health advisory for manganese in drinking water. The lifetime health advisory to protect against chronic neurologic impacts is at 0.3 mg/L. This lifetime advisory is also used for short-term exposure to infants and children due to their sensitive life stage. The acute exposure advisory for adults is 1.0 mg/L. These levels are significantly above the 0.05 mg/L SMCL for manganese. When the department sees results for manganese above one or both of these health advisory levels, we utilize our authority under the public notice rule to require water systems to notify the public about the health risks. But because there is no primary MCL for manganese, we do not require compliance with the health advisory levels.
However, manganese levels above the secondary standard, which are often accompanied by high iron levels, can make drinking water quality very problematic for customers and water utilities. Customers may sometimes experience black or dark-colored water with sediment. The water can cause problems with appliances and laundry, via staining clothes. For water utilities, high iron and manganese levels can clog distribution piping, reducing available pipe volume and increasing the need for flushing and maintenance. We have seen situations where high manganese and iron levels impact distribution systems so much that significant deficiencies are created.
In general, customers do not trust or want drinking water that exceeds secondary standards, especially when they can see, smell, or taste the problems. But water utilities and their customers share concerns for the potential cost of addressing this problem. One thing to consider is that problems like this tend to only get worse and more expensive to address over time. Another consideration is pursuing funding assistance. Manganese is considered an emerging contaminant, and we have dedicated funding to help address this issue. If your water utility has manganese, iron, or other problems with SMCLs please reach out and work with us to explore options to address the situation.
Again, thanks for all you do to keep tap water safe in Colorado.
➽ Ron Falco, P.E, Safe Drinking Water Program Manager
