Walkerton water was adequately pure and safe without a 0.5 mg/L chlorine residual—they were known to willingly drink raw water from the wells—and they had received complaints from community members about system water tasting overly chlorinated. The PUC's evaluation of chlorine residual levels was typically performed weekly, rather than daily, and actual testing was often eschewed in favour of visually inspecting the "bubble" on the chlorinator for a "guesstimate" of the residual. These "guesstimates" would be noted in the PUC's daily operating sheets as if they were actual tested levels. When actual testing was performed, the 15-minute timeframe of the test was often cut short, resulting in higher-than-reality chlorine residual readings. Fecal coliform and E. coli testing on Well 5 between 1990 and 2000 showed ongoing deterioration in the quality of water from the well. In the mid-1990s, a provision for more intensive monitoring of wells susceptible to groundwater contamination was added to the Ontario Drinking Water Objectives (ODWO); however, the Ministry of the Environment (MOE) failed to apply this provision to reclassifying existing wells. As a result, despite tests repeatedly showing that Well 5 was prone to contamination, it did not have any contamination alarms or emergency shut-off mechanisms. April 2000 sampling done on water from Wells 5 and 6 showed fecal coliform present in Well 5's water, both raw and treated, but not in Well 6's. Well 7 was not running during this time period and was not tested. May 1, 2000 tests showed similar results, with Well 5 being the sole apparent contaminated water source. May 15 water testing on the Highway 9 water main construction project in Walkerton returned positive results for fecal coliform and E. coli. Due to inaccurate labelling of the samples' sources by PUC personnel, it was unclear to the testing laboratory which water samples had come from Walkerton's raw water versus its treated water, or which water had come from which well source; however, the laboratory notified Stan Koebel on May 17 that submitted samples had tested positive for E. coli and fecal coliform. Personnel from the testing laboratory, unaware that Ontario Drinking Water Objectives mandated the notification of the Ministry of the Environment in such a case, did not notify any agency besides the PUC of the failed testing results. Contamination period Using knowledge about typical incubation periods of E. coli O157:H7 (average 3–4 days) and Campylobacter (average 2–5 days) bacteria