- Picture free chlorine as a 100% ready-for action superhero that cannot wait to wipe out just about any biological contaminant it encounters. It has both hands free and ready to fight.
- Picture combined chlorine as that very same superhero after it wrestled and defeated a biological contaminant. The two ‘locked horns’ and now cannot separate despite the superhero having won the fight. The superhero can still attack other biologicals, but think of it now as having only one of its hands free to attack other biologicals… and thus it cannot fight as effectively.
OK, So What is This Total Chlorine?
Simply put, total chlorine is the sum of the free chlorine plus combined (used) chlorine in the water. See the following equation:
The USEPA has set the Maximum Contaminant Level (MCL) for TOTAL chlorine in potable water at 4.0 ppm.
This means water dispensed by a water system must contain less than 4.0 ppm total chlorine… or the system is in violation of Federal Law and subject to getting fined and/or shut down by the USEPA if their total chlorine readings continue to exceed Federal Guidelines.
As a general rule, most water treatment facilities use a method called “DPD Testing” to determine the chlorine concentrations in drinking water. Other methods for testing exist, though most are not officially approved by the USEPA and may not be used for reporting purposes.
As of Spring 2007, though, the USEPA began allowing states to approve the use of an alternate, yet equal, faster method called SenSafe(tm) Free Chlorine Water Check when testing for free chlorine residual.
That same company also manufactures a dip-n-read test strip for total chlorine referenced by the USEPA only as a screening method for total chlorine concentrations in wastewater. [see Federal Register / Vol. 72 No. 47 / Monday, March 12, 2007 / Rules and Regulations]
Testing for Combined Chlorine?
You may also see combined chlorine called ‘chloramines’ in certain literature and some water systems actually use them to sanitize/disinfect the water they supply. Though not as effective a killing tool as free chlorine, they do get the job done.
If you wish to test for chloramines, you only need to perform two very simple tests and do some really easy subtraction: