Table 2.

Results of logistic regression used to evaluate factors that affect water potability in the Apulia region

	UNIVARIATE			MULTIVARIATE
	p value	OR	95 % CI	p value	OR	95 % CI
COMPULSORY PARAMETERS
Season:
autumn-winter vs. spring-summer	<0.0001	2.2	1.8–2.8	<0.0001	2.1	1.6–2.7
Aquifer:
karst vs. porous	<0.0001	4.8	3.6–6.4	<0.0001	5.8	4.4–7.8
Area:
Gargano vs. Arco Jonico	0.0003	1.5	0.8–3.1	Not entered
Tavoliere vs. Arco Jonico	0.0011	1.9	1.1–3.6
Murgia vs. Arco Jonico	<0.0001	11	6.3–19.4
Salento vs. Arco Jonico	<0.0001	8.6	4.8–15.3
OPTIONAL PARAMETERS
Season:
autumn-winter vs. spring-summer	0.0007	1.8	1.3–2.6	<0.0001	2.6	1.7–3.9
Aquifer:
karst vs. porous	0.2703	1.2	0.8–1.7	Not entered
Area:
Gargano vs. Arco Jonico	0.339	0.8	0.4–1.6	Not entered
Tavoliere vs. Arco Jonico	0.2112	0.8	0.5–1.5
Murgia vs. Arco Jonico	0.2505	0.9	0.5–1.5
Salento vs. Arco Jonico	0.0039	1.7	0.9–3.2

The odds ratio (OR) expresses the probability of potability with respect to a reference class. The reference classes are spring–summer for season; porous for aquifer type; and Arco Jonico for area