TABLE 4.

Change in sampling site-specific parameters between the chlorine phase and the monochloramine phase

Parameter	Value for hot water heaters			Value for distal sites
	CL phase	MC phase	P valuea	CL phase	MC phase	P value
Total chlorine detectable, no. (%)	72 (75.8)	77 (81.0)	1.0	70 (76.1)	77 (81.9)	0.21
Free chlorine detectable, no. (%)	59 (61.5)	0 (0)	<0.0001	60 (63.8)	0 (0)	<0.0001
MC detectable, no. (%)	0 (0)	85 (88.5)	<0.0001	0 (0)	87 (92.6)	<0.0001
Temp categoryb
<26°C	4 (4.2)	2 (2.1)	0.61c	2 (2.2)	1 (1.1)	0.54c
26-42°C	35 (36.5)	39 (40.6)		28 (30.8)	35 (37.2)
>42°C	57 (59.4)	55 (57.3)		61 (67.0)	58 (61.7)
Mean temp (°C)	43.6	44.1	0.72d	44.1	43.5	0.57d
Mean pH	7.6	7.7	0.05d	7.7	7.7	0.19d
Mean conductivity (μS/cm)	533.7	503.8	0.12d	518.7	498.7	0.07d
No. of sample locations with Legionella	9 (9.4)	4 (4.2)	0.062	13 (13.8)	4 (4.3)	0.004
No. of sample locations with amoebae	2 (2.0)	2 (2.1)	1.0	11 (11.7)	14 (14.9)	0.25

^aP value comparing the value for CL phase to the value for MC phase by McNemar's test unless otherwise indicated.

^bCategories indicate temperatures favorable (26 to 42°C) and unfavorable (<26°C and >42°C) for Legionella growth.

^cBy Fisher's exact test.

^dBy t test.