Table 3.

Elemental concentrations of waste and clean water in Tamale and Ouagadougou. Means over all crops ± SD (in italics).

	N 1	PO 4 -P	Ca 2+	Mg 2+	K +	Na +	pH
	mg l−1	mg l−1	mg l−1	mg l−1	mg l−1	mg l−1
Tamale
Clean water	0.4	0.1	9.4	2.3	1.7	2.0	7.4
	0.2	0.0	1.9	0.6	0.9	0.8	0.7
Waste water	31.9	8.9	28.2	6.0	8.4	19.2	7.6
	14.6	6.3	5.8	0.6	5.7	3.9	0.7
Ouagadougou
Clean water	0.8	0.2	15.7	3.7	8.2	6.0	8.3
	0.8	0.0	9.1	1.6	2.9	2.1	0.5
Waste water	3.9	0.8	22.5	4.8	44.0	38.8	8.4
	1.5	0.3	4.5	1.8	29.7	17.7	0.6

¹N = NO₃-N + NH₄-N.