Water Term Defininitions

MAC
MAXIMUM ACCEPTABLE CONCENTRATION, is a health standard known to have adverse effects.

IMAC
INTERIM MAXIMUM ACCEPTABLE CONCENTRATION
, suspected adverse health effects but not feasible for practical reasons to establish a MAC

Adverse Test Result
Is a test that fails, where the results exceed the MAC or IMAC, and retesting and boil water advisories must be issued.

Absent
Means that no traces were found in the sample submitted for testing.

E. Coli
Escherichia coli. is a fecal coliform that can be detected by using membrane filtration or presence/absence tests and should not be detected in any drinking water sample. Because E coli. is rapidly destroyed by chlorine, it is a good indicator of recent fecal pollution.

Heterotrophic Plate Count
HPC, A laboratory procedure for estimating the total bacteria count in a water sample. Also called standard plate count, total plate count, or total bacterial count. The sample is incubated for 48-72 hours, MAC of 500 colonies /milliliter. The only practical way to determine the total population of bacteria in the water.

Background Bacteria
Bacterial aftergrowth, bacteria reproducing in the system after it has been treated, usually in stagnant water in dead ends, or low flow sections of the water distribution system. The Standard Plate Count determines whether this problem exists.

Total Coliforms
The detection of coliform bacteria in a water sample is a warning of possible contamination. One positive test does not conclusivly prove contamination, hawever, additional tests must be done. The samples may have been contaminated by improper sampling, or laboratory error, therefore repeat sampling must be done.

Chlorine Residual
Is the amount of free chlorine and chlorine compounds in the distribution system available to kill or inactivate any microorganisms present or introduced to the water supply after it leaves the treatment plant. A chlorine residual of 0.2 mg/l measured at the exreme ends of the distribution system is a good indication that chlorine residual is available.

Trihalomethanes
Can be formed when organic materials are present in the water being disinfected with chlorine. Trihalomethanes are suspected carcinogenic compounds. Therefore there is a MAC of .10mg/liter on a 4 quarter rolling average.