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Table 1 Characteristics of water-sampled homes, overall and by type of water supply

From: Water quality monitoring records for estimating tap water arsenic and nitrate: a validation study

  All homes
N = 107
Public system*
N = 89
Private well
N = 18
  n (%) n (%) n (%)
Within city/town limits 56 (52) 55 (62) 1 (6)
Type of water supply    
   Public system 89 (83) 89 (100) --
Municipality 63 (59) 63 (71) --
Utility district 12 (11) 12 (13) --
Private utility/association 14 (13) 14 (16) --
   Private well 18 (17) -- 18 (100)
Shared 7 (7) -- 7 (39)
Individual 11 (10) -- 11 (61)
Water source    
Groundwater 73 (68) 55 (62) 18 (100)
Surface 34 (32) 34 (38) 0 (0)
Arsenic level    
Any detected 97 (91) 82 (92) 15 (83)
> MCL 0 (0) 0 (0) 0 (0)
  μg/L μg/L μg/L
Minimum 0 0 0
25th percentile 0.35 0.35 0.41
Median (μg/L) 0.59 0.56 1.31
75th percentile 1.24 0.97 1.94
Maximum (μg/L) 9.5 4.34 9.5
Nitrate level§ n (%) n (%) n (%)
Any detected 76 (72) 64 (74) 12 (67)
> MCL 2 (2) 0 (0) 2 (11)
  mg/L as N mg/L as N mg/L as N
Minimum 0 0 0
25th percentile 0 0 0
Median (mg/L) 0.37 0.35 0.39
75th percentile 1.65 1.52 2.27
Maximum (mg/L) 40.5 4.48 40.5
  n (%) n (%) n (%)
Nitrite, any detected§ 0 (0) 0 (0) 0 (0)
  1. * Water system served by wells, surface sources or other sources with federally-mandated monitoring; represented systems served 95 to > 600 000 homes; water came directly or via intermediate purveyors from one of 55 water suppliers, including 12 serving multiple (≤ 12) sampled homes.
  2. † Individual or shared (2-8 homes) private well, not subject to federally-mandated monitoring.
  3. ‡ Current U.S. federal maximum contaminant level (10 μg/L arsenic and 10 mg/L nitrate as nitrogen).
  4. § As nitrogen, among 105 for whom nitrate and nitrite values were determined.