Wholesale suppliers or purchasers of finished water Systems who purchase all of their finished surface water or groundwater from another PWS are not subject to the Stage 1 DBPR, but will be subject to the Stage 2 DBPR, and hence most will have to conduct an IDSE. In the new regulation, PWSs that supply some or all of their finished water to another PWS are called “wholesale systems”, a PWS that purchases some or all of their water from another system is called a “consecutive systems” (note that one consecutive system could purchase its water from a wholesale system or another consecutive system), and one or more wholesale systems connected to one or more consecutive systems are called a “combined distribution system” (CDS). According to USEPA, all States have already identified all possible CDS combinations in their state, and USEPA has subsequently assigned a unique identification number to each CDS. If your PWS has an emergency or seasonal interconnection to another system, or if this interconnection does not represent a significant volume or percentage of all the water used by your PWS, it is possible you have not been identified as a CDS. If you are unsure about whether you have been designated as part of a CDS you should check with your state. If you are part of a CDS, all PWS associated with the CDS must comply with the compliance schedule of the largest PWS in the CDS (i.e., a CDS including two PWSs serving 30,000 each and another serving 60,000 would all have to comply with the schedule for systems >50,000). Some consecutive systems that purchase all of the finished water they use, especially those that are small systems, may not have been collecting Stage 1 DBPR samples. Hence they may not be eligible for the 40/30 or VSS exceptions mentioned in an earlier paragraph (unless they complete voluntary Stage 1 DBPR monitoring at a monitoring location (or locations) approved by the State prior to the Stage 2 DBPR deadline required for systems of their size). Each system in a CDS is responsible for their own IDSE and for later collection of Stage 2 DBPR compliance samples. However, it is possible that many small systems will seek out assistance from larger systems in a CDS if suitable arrangements can be developed to the satisfaction of all parties involved (i.e., help with sample collection, analysis, modeling, or preparation of the smaller PWS’s IDSE related reports). Note that the largest PWS in your CDS establishes compliance dates, but does not have any bearing on the number of samples associated with your PWS. Consequently, if your PWS serves a population of 30,000 and two other PWSs in your CDS are 30,000 and 60,000 respectively, all three PWSs must comply with the compliance date for systems >50,000 but your PWS only needs to collect the number of samples required for systems serving 10,000 to 49,999 people (i.e., 8 locations if you are supplied with surface water (or a mixture of groundwater and surface water) and 6 locations if you are supplied by groundwater only). Last Updated: January 25, 2006