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

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

	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
25^th percentile	0.35	0.35	0.41
Median (μg/L)	0.59	0.56	1.31
75^th 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
25^th percentile	0	0	0
Median (mg/L)	0.37	0.35	0.39
75^th 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)

* 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.
† Individual or shared (2-8 homes) private well, not subject to federally-mandated monitoring.
‡ Current U.S. federal maximum contaminant level (10 μg/L arsenic and 10 mg/L nitrate as nitrogen).
§ As nitrogen, among 105 for whom nitrate and nitrite values were determined.

ISSN: 1476-069X