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Source Water Monitoring Rule


The purpose of the rule is to ensure adequate treatment of surface water sources with higher levels of Cryptosporidium and to address uncovered finished water reservoirs. The rule applies to all public water systems that use surface water or groundwater under the direct influence of surface water (GWUDI).

Rule Summary

Two rounds of source water monitoring are required for all surface water and GWUDI systems. 

  • Filtered systems serving 10,000 or more people: Monthly monitoring of raw water for Cryptosporidium, E. coli and turbidity is required for 2 years, according to the dates in Table 1, below.
  • Filtered systems serving less than 10,000 people: Raw water must be sampled for E. coli every 2 weeks for one year. If the running average of the results is above a trigger level (100 counts per 100 ml), the system must sample for Cryptosporidium monthly for 2 years. Systems can also choose to sample for Cryptosporidium in lieu of E. coli.
  • Systems can avoid source water monitoring if they provide at least 5.5-log (filtered) or 3-log (unfiltered) Cryptosporidium treatment.
  • New systems or sources must begin source water monitoring on an approved schedule.
  • Grandparenting of data is allowed to substitute for the first round of sampling if similar methods were used and sampling took place over multiple seasons.
  • PDF iconList of ORELAP accredited Cryptosporidium and E. coli enumeration labs (pdf)

Systems must report data monthly. Source water monitoring must begin by the start dates shown in Table 1:

Table 1. Source Water Monitoring Start Dates

Systems that serve.... Must begin the first round of source water monitoring no later than the month beginning.... And must begin the second round of source water monitoring no later than the month beginning...
At least 100,000 people October 1, 2006 April 1, 2015
From 50,000 to 99,999 people April 1, 2007 October 1, 2015
From 10,000 to 49,999 people April 1, 2008 October 1, 2016
Fewer than 10,000 people and monitor for E. coli (filtered systems only) October 1, 2008 October 1, 2017
Fewer than 10,000 and required to monitor for Cryptosporidium April 1, 2010 April 1, 2019
  • Based on average Cryptosporidium concentrations, systems are classified in Bins 1 through 4 as shown in Table 2:

Table 2. Bin Classification

Mean Cryptosporidium Concentration Bin Classification
< 0.075 Cryptosporidium oocysts/L, including water systems serving fewer than 10,000 people OR all systems not required to monitor for Cryptosporidium (did not exceed E. coli trigger). Bin 1
= 0.075 oocyst/L to < 1.0 oocysts/L Bin 2
= 1.0 oocysts/L to < 3.0 oocysts/L Bin 3
= 3.0 Cryptosporidium oocysts/L Bin 4
  • Bin classification determines how much additional Cryptosporidium treatment is required, as shown in Table 3:

Table 3. Treatment Required

Type of SWTR Filtration Treatment and Cryptosporidium Treatment Requirement
Slow Sand or
DE Filtration
1 No additional treatment No additional treatment No additional treatment No additional treatment
2 1-log treatment 1.5-log treatment 1-log treatment Total must be 4.0 log
3 2-log treatment 2.5-log treatment 2-log treatment Total must be 5.0 log
4 2.5-log treatment 3-log treatment 2.5-log treatment Total must be 5.5 log
  • Unfiltered systems also have to sample for Cryptosporidium. Systems with a population ≥10,000 sample monthly for 24 months, and those with population <10,000 sample either on the 12 month or 24 month schedule. They also must provide either 2- or 3-log removal or inactivation, depending on the average concentration. At least two disinfectants must be used, with each providing the total inactivation required for either Cryptosporidium, Giardia lamblia, or viruses.
  • LT2 provides a "Toolbox" of options for Cryptosporidium treatment and the log reduction assigned to each.
    • There are 16 options listed in the toolbox, including watershed protection program, bank filtration, presedimentation with coagulation, improved filtration performance (conventional), additional filtration (membrane, cartridge, conventional, or slow sand), ozone and UV. Log reductions are assigned to each toolbox option, or systems can demonstrate a higher log reduction.
    • The rule requires extensive requirements as to the challenge studies for cartridge and membrane filters, as well as for validation studies for UV. Membrane and cartridge filters that were installed prior to May 18, 2009 do not have to re-submit their challenge study and will not be re-reviewed. Anything going in after that date must have a challenge study that meets the protocol specified in the construction standards, regardless of whether the treatment is being installed for LT2 or any other surface water treatment rule. A list of acceptable membrane and cartridge filters is located on our website here.
    • For membrane filtration, laser turbidity or particle counting is no longer required. The new requirement is for a regular turbidimeter after each filter unit (defined as having joint piping), as well as a combined effluent turbidimeter. If the IFE turbidity is greater than 0.15 NTU, a direct integrity test must be done immediately.
  • If additional Cryptosporidium treatment is required, systems must comply by the dates shown in Table 4. An additional 2 years beyond these dates is allowed if capital improvements need to be made.

Table 4. Deadlines for Additional Treatment

Systems that serve... Must comply with
Cryptosporidium treatment by:
= 100,000 people April 1, 2012
From 50,000 to 99,999 people October 1, 2012
From 10,000 to 49,999 people October 1, 2013
Less than 10,000 people October 1, 2014

  • All finished water reservoirs and groundwater treatment basins must be covered or the effluent treated to 3-log Giardia lamblia, 2-log Cryptosporidium, 4-log virus reduction. Abandoning the reservoir is also an option.