Quality assessment of rainwater and harvested rainwater stored in different types of cisterns

Abstract

Rainwater is widely collected and stored in cisterns for domestic use due to extreme water scarcity and poor water quality on the Loess Plateau, China. However, little information exists on the effects of cistern materials and construction methods on water quality. This study assessed the quality of rainwater and harvested rainwater stored in different types of cisterns, using multivariate statistical analysis techniques. The harvesting system consisted of ditches underground to direct the water stream collected by catchments through pipes to the two-stage grit chambers, the rainwater runoff ultimately being fed into the cisterns. Water samples were collected monthly over 6 months from October 2008 to April 2009. The harvested rainwater generally did not meet drinking water standards due to severe bacterial contamination. To determine the factors affecting water quality, principal components and factor analysis divided the water's physicochemical composition into four principal components: ions, suspended pollutants, reducing substances, and acidity-alkalinity, which collectively accounted for 80.4% of the total variance. Cluster analysis confirmed the results. It was determined that pollutants in harvested rainwater were mainly derived from the catchments, surrounding fields, and local atmosphere. Furthermore, factor scores ranked water quality to select the optimum material and construction method. It was concluded that cement was superior to stabilized soil for rainwater storage. However, considering water quality, cost, and environmental friendliness the stabilized soil cistern using the stiff construction method was worthy of consideration.