Sampling Procedure: Remove any attachments from the sample tap, such as hoses, filters, screens, or aerators, and disinfect the sample tap by spraying the sample tap thoroughly with Isopropyl alcohol (91%). Allow to air dry for 2 minutes. Flush the sample tap for 5 minutes until the water temperature reaches a constant temperature, and then reduce water flow to a smooth (laminar) stream about the size of a pencil if possible. The disinfectant (chlorine) residual must be measured at the time of collection for the total coliform sample at the LDH/OPH-approved sample sites (e.g., TCR-001, MRT-001, etc.) in the Public Water Systems (PWS) distribution system. The disinfectant (chlorine) residual must be measured using an LDH/OPH-approved N,N-diethyl-p-phenylenediamine (DPD) colorimeter (e.g., HACH Colorimeter). Measure the residual type (free or total) that is specified for the water system. Total chlorine is measured for systems that use chloramines. Measure the residual using an appropriate method, taking into account any interfering substances that may be present. For example, both manganese and chloramine can interfere with the DPD colorimetric method, but do not interfere with the indophenol method. As a result, for systems that operate using free chlorine, that have manganese and/or naturally occurring ammonia, the indophenol method or a DPD method that specifically accounts for the interference of concern should be selected...
