Rainwater Quality as a Function of Time of Harvest

Abstract

Rainwater samples were collected at five minute intervals up to 25 minutes and assessed for physicochemical, total coliform load and some heavy metals. This was aimed at evaluating the purity of the rainwater through the progress of the rain duration. The result of temperature for the three months was found to range from 21.9 - 23.4 25oC, pH was found to range between 6.0-6.20, turbidity was observed to range between 0.67-2.11NTU. Conductivity was observed to range from 2-7 µs/cm, total hardness was constant be 20 mg/L, while total dissolved solids was found to be between 1 to 2 mg/L. Total suspended solids range between 36 to 62 mg/L. The mean values of BOD and COD were found to range between 0.1- 0.80 mg/L and 0.4-1.6 mg/L respectively. Chloride and sulphates were found to range between 102 mg/L to 112 mg/L and 7 to 9 mg/L respectively. Phosphates and nitrates were found to range between 0.13mg/L to 0.60 mg/L and 2.0 mg/L to 3.0mg/L respectively. Result of total coliform count was negative in all samples. Varying concentrations of heavy metals was observed; Zn (0.159 - 0.30) mg/L, Cadmium, lead, aluminum and iron were found to range between 0.009-0.11mg/L, 0.001 - 0.002 mg/L, 0.006-0.016 mg/L and 0.154-0.224 mg/L respectively. Nickel and chromium were not detected. The concentrations of heavy metals were observed to be very low compared to WHO permissible limits and Nigerian National Agency for Food and Drug Administration and Control. All parameters analyzed were observed to decrease as the time of the rainfall increases.