Variations in rainwater quality from roof catchments

Abstract

The quality of rainwater from a tile and a galvanized-iron type roof catchments were analysed over a period of 5 months. Examination of staggered I litre samples collected during a rainfall event showed that the concentration of various pollutants were high in the first litre but decreased in subsequent samples with few exceptions. Faecal coliform and total coliform counts ranged from 8-13 (tile roof) and 4-8 (iron roof) to 41-75 (tile roof) and 25-63 (iron roof) colonies per 100 ml, respectively. However, no faecal coliforms were detected in the fourth and fifth litre samples from both roofs. The pH of rainwater collected from the open was acidic but increased slightly after falling on the roofs. The average zinc concentrations in the run-off from the galvanized-iron roof was about 5-fold higher compared to the tile roof, indicating leaching action but was well below the WHO limits for drinking water quality. Lead concentrations remained consistently high in all samples collected and exceeded the WHO guidelines by a factor of 3.5. For the roof area studied, a "foul flush" volume of 51. would be the minimum to safeguard against microbiological contamination but the high metals content in the water indicate the need for some form of treatment. Rainfall intensity and the number of dry days preceeding a rainfall event significantly affects the quality of runoff water from the catchment systems.

Physiochemical characteristic of Harvested Rain water from Bodo Community in Rivers State, Nigeria

“…The pH values of most samples analyzed were below the WHO allowable limit for portable water (6.5-8.5) except water samples from aluminum roofing sheet that fell within WHO allowable limit. The pH values obtained in this study agreed with the result of Yaziz et al, (1989) and Simmons et al, (2001) with reported pH of 5.2 to 11.4 for harvested rainwater.…”

Quality of Roof-Harvested Rainwater as a Function of Environmental and Air Pollution Factors in a Coastal Mediterranean City (Haifa, Israel)

“…The results indicated a decrease in FC concentration during long breaks between consecutive rain events. This is in contrast to many other studies, reporting that longer dryweather periods result in higher microorganism levels, due to the increased deposition of animal faeces on the roof surface (e.g., [24]). This discrepancy most likely stems from the limited number of FC measurements (51 samples, representing 17 rain events, in 25% of which FC was undetected) and the generally low FC concentrations, much lower than values reported in the literature (e.g., [14,25]).…”

The contribution of particles washed from rooftops to contaminant loading to urban streams

“…While many investigators have demonstrated that concentrations of contaminants in rooftop runoff exceed drinking-water guidelines or have documented the toxicity of rooftop runoff to aquatic organisms (e.g., Yaziz et al, 1989;Good, 1993;Thomas and Greene, 1993), the results described here indicate that particle-bound contaminants washed from rooftops may contribute to sediment toxicity in receiving water bodies. Particles in some rooftop washoff …”