Evaluating the Effectiveness of Point-of-Entry UV Treatment for Cistern Water Among Households in the US Virgin Islands

Abstract

UV water treatment can be a viable option for point-of-entry applications among households utilizing private water sources. In the US Virgin Islands (USVI), the primary water source is roof-harvested rainwater, collected in large cisterns and supplied to household taps via a pump. While diversification of water sources provides increased resilience to climate change, literature suggests rainwater catchment systems are at high risk of microbial contamination. One option USVI households have is UV systems. However, limited data is available on UV system effectiveness for USVI installations while these systems can be expensive. Therefore, Love City Strong, a local NGO, piloted a multi-year UV access program which included free UV systems with prefiltration along with installation and monthly household visits for up to 12 months including water quality testing. In addition, due to the significant costs associated with the prefiltration portion of the system, a pilot study was conducted to evaluate the effectiveness of the UV systems without prefiltration.The results from the UV system access program demonstrated thatE. coliwas not detected in 95.2% of tap samples (n=271). Among samples with detectable levels ofE. coliand total coliforms, turbidity was lower compared to samples with non-detections. Field teams reported user error was often identified in association withE. colidetections (e.g., bypass was opened). Among all samples from the pilot study of UV systems without prefiltration, noE. coliwas detected (n=24). Total first-year costs for locally available UV systems with and without prefiltration ranged from $1,059-$1,645 and $927-$1,183, respectively, while operation and maintenance (O& M) costs ranged from $166-$266 and $142-$146, respectively. Given these data, UV systems may be a viable option for generating potable water; however, clear purchasing and installation protocols are needed as well as simple O&M guidelines for households to reduce user error.SynopsisPoint-of-entry UV systems were able to produce water for domestic use with no detectable E. coli in 95.2% of samples among USVI households using roof-harvested rainwater.