Microbial hazards in rainwater harvesting systems: bacterial sources, indicators, and health implications - a review

Rainwater harvesting systems (RWHS) are an important element of sustainable water management in urbanized areas, by supporting retention and adaptation to climate change. The widespread use of RWHS, however, is limited due to concerns about the microbiological purity of the water. The aim of the review is to illustrate the current state of knowledge regarding microbiological hazards and methods of their assessment in the rainwater of RWHS.

A comprehensive literature search was conducted using Scopus, ScienceDirect, and PubMed databases. Publications from 2000-2026 were analyzed, with special consideration of the studies published after 2015. Key words included: rainwater harvesting, RWHS, microbiological contamination, faecal indicator bacteria, FIB, microbial source tracking, MST, quantitative microbial risk assessment, QMRA.

RWHS systems are an effective tool for rainwater management and protection of its resources in integrated water resource management systems. However, the fundamental limitation to their broader implementation is mainly microbiological hazards, effectively limiting the use of rainwater for domestic and consumption purposes.

The review organizes the knowledge on the safety of water from RWHS, considers microbiological hazards, FIB indicator bacteria, markers for identification of sources of microbiological contamination (MST), and QMRA microbiological risk assessment methods. It also discusses the limitations associated with FIB, the significance of MST, and the role of QMRA. Current data indicate that untreated water from RWHS is often suitable for use in non-consumption activities; however, it usually exceeds the standards set for drinking water. The water from RWHS intended for drinking most often requires treatment and continuous monitoring.