MBAS FACT SHEET
(Methylene blue active substances) used to detect detergents and foaming agents
Acceptable Level: 0.5 mg/L MCL, Secondary Drinking Water Standard
Household and Industry Usage
Causes water to foam and have a bad taste
Test for MBAS
Eliminate the source if possible. Activated carbon filter.
Source: Detergents enter the environment from household and industry usage. Detergents are a
contaminant found in the National Secondary Drinking Water Regulations. The EPA does not enforce these
“secondary maximum contaminant levels.” They are established only as guidelines to assist public water
systems in managing their drinking water for aesthetic considerations, such as taste, color, and odor. These
contaminants are not considered to present a risk to human health at the secondary maximum contaminant
The EPA believes that if these contaminants are present in your water at levels above these standards, the
contaminants may cause a great number of people to stop using water from their public water system even
though the water is actually safe to drink.
Secondary standards are set to give public water systems some guidance on removing these chemicals to
levels that are below what most people will find to be noticeable. These problems include: aesthetic,
cosmetic, and technical effects.
Aesthetic effects – undesirable tastes or odors.
Cosmetic effects – effects which do not damage the body but are still undesirable.
Technical effects – damage to water equipment or reduced effectiveness of treatment for other contaminants.
Foaming is usually caused by detergents and similar substances when water has been agitated or aerated as in many faucets. An offtaste
described as oily, fishy, or perfume-like is commonly associated with foaming. However, these tastes and odors may be due to
the breakdown of waste products rather than the detergents themselves.
Problems associated with Detergents include but are not limited to: frothy, cloudy, bitter taste; odor may indicate contamination
from drain fields or wash water runoff. Other contaminants may be present if this is the case.
Effect: Short-term: potentially undesirable tastes, odors, and/or staining.
Follow up: Treat and re-test for MBAS
Treatment: Depending on the cause, there are treatment options that range from simply locating and
eliminating the source, to treating with chlorine for waste-water issues, to installing an activated carbon filter
which can remove low levels of detergent.
Following installation of this system, the consumer should have the treated water tested for MBAS to
verify MBAS reduction is being achieved and the system is functioning properly. For more information
visit the USEPA web site:
MBAS FACT SHEET