Risk-based treatment targets for onsite non-potable water systems using new pathogen data.

Area of Science:

• Environmental Engineering
• Public Health
• Water Resource Management

Background:

• Decentralized water reuse systems, utilizing sources like roof runoff and graywater, offer solutions for potable water reduction and supply reliability.
• California mandated risk-based regulations for onsite non-potable water systems (ONWSs) following a 2017 framework.

Purpose of the Study:

• To update pathogen log reduction targets (LRTs) for ONWSs using current quantitative data.
• To propose effective treatment trains for meeting updated LRTs.
• To expand the range of end-uses for non-potable water applications.

Main Methods:

• Convening a California Expert Panel in 2021.
• Analyzing new quantitative pathogen data for viruses, protozoa, and bacteria.
• Evaluating risk-based frameworks for multiple source waters and end-uses.
• Estimating costs and footprint for ONWS implementation.

Main Results:

• Updated 95th percentile LRTs were developed for various pathogens, source waters, and end-uses (e.g., toilet flushing, irrigation).
• LRT requirements showed minimal deviation (typically within 1-log10) from 2017 targets.
• Pathogen reduction requirements decreased as influent pathogen levels decreased from wastewater to roof runoff.

Conclusions:

• The updated LRTs provide a refined, risk-based approach for regulating ONWSs in California.
• The findings support the safe and reliable use of diverse local water sources for non-potable demands in buildings.
• Cost and siting considerations are integral to the practical implementation of ONWSs.