Summary of the World Health Organization's Water Reuse Guideline or Regulation for Potable Water Reuse
This page is part of the EPA’s REUSExplorer tool, which summarizes the different state level regulations or guidelines for water reuse for a variety of sources and end-uses.
The source water for this summary is Treated Municipal Wastewater.
On this page:
- Technical basis
- Types of potable reuse in WHO guidance
- Water reuse treatment category/type
- Additional context and definitions
- Potable water reuse specifications (table)
- References
- Disclaimer
This page is a summary of the organization’s water reuse law or policy and is provided for informational purposes only. Please always refer to the organization for the most accurate and updated information.
The World Health Organization provides guidance for potable water reuseThe use of highly treated recycled water for drinking water purposes. Includes the introduction of recycled water into an environmental buffer, such as groundwater aquifer or surface reservoir being withdrawn for potable purposes (indirect potable reuse), and the introduction of recycled water into a drinking water treatment facility or directly into a potable water distribution system (direct potable reuse). applications including indirect potable reuse and direct potable reuse. The source of water treated municipal wastewater Treated wastewater effluent discharged from a centralized wastewater treatment plant of any size. Other terms referring to this source of water include domestic wastewater, treated wastewater effluent, reclaimed water, and treated sewage. is specified by the organization as treated wastewater. The write-up on this page uses the organization’s terms when discussing sources or uses of water that may differ from the Regulations and End-Use Specifications Explorer's (REUSExplorer's) terms.
Technical basis
The World Health Organization (WHO) provides guidance for potable water reuse, as an international reference point for those seeking to develop regulations. Like all water supplies, WHO recommends ensuring the consistent supply of safe drinking water through the application of a framework that comprises health-based targets, effective risk assessment and management and independent surveillance. The 2017 WHO Potable Reuse document provides detailed guidance on considerations for applying this framework for producing safe drinking water from treated municipal wastewater (WHO, 2017). These health-based targets are measurable microbial, chemical and radiological parameters. For example, microbial log-reduction values (LRV), chemical concentrations and radioactivity levels based on risk estimates that define drinking water safety used in the 2022 WHO Guidelines for Drinking Water (GDWQ) (WHO, 2022). These health-based targets apply regardless of the drinking water source, including potable water reuse of treated municipal wastewater and allow the risk assessment of microbial, chemical and radiological hazards that could be present in wastewater. As a result, the targets include four forms: water quality, treatment performance, technology-specific targets and health outcomes. These targets should be set by national or regional authorities in collaboration with drinking water suppliers and other relevant stakeholders according to their particular economic, social and technical feasibility conditions and should be based on health outcome targets set by public health authorities and drinking water regulators. Performance targets are used for pollutants where short-term exposure to highly variable concentrations can lead to significant health impacts, and these targets typically apply to microbial hazards (WHO, 2022; WHO, 2017). For example, potable water use of treated municipal wastewater will typically have higher LRV targets compared to other sources of drinking water since wastewater contains higher concentrations of pathogens.
A Disability-Adjusted Life Year (DALY) approach for setting health-based targets is not currently used in the United States. However, the WHO recommends use of the DALY approach to set health-based microbial LRV targets. DALYs are used to weigh health impacts in terms of severity and duration of disease and the number of people affected. One DALY is equivalent to the loss of one year of full health and it is the sum of years of life lost due to premature mortality (YLLs) and years lived with a disability (YLD) associated to a specific disease or health condition prevalence (WHO, 2023). The WHO guidelines for drinking water define a tolerable burden of disease of 10-6 DALYs per person per year (pppy) (WHO, 2022). In drinking water, DALYs are primarily used for microbial hazards, with 10-6 DALYs pppy being approximately equivalent to 1 case of diarrheal disease per 1,000 people per year, differing from, e.g., California, that has a health-based target of less than 1 infection (with or without diarrheal disease) per 10,000 people per year. Similarly, 10-6 DALYs pppy is approximately equivalent to a cancer risk of 1 excess case per 100,000 people from lifetime exposure to a chemical carcinogen. The resulting log reductions for microbial contaminants can be different from other approaches depending on the pathogen-specific relative severity of illness. For example, norovirus has a high probability of infection but low illness severity which can account for much of this difference between approaches. WHO indicates that regulators in each country may choose to adopt the 10-6 DALYs pppy as a target or have an alternative target depending on local circumstances, including overall burdens of disease. The principles and health-based targets in the GDWQ (WHO, 2022) also apply to potable water reuse just as they do to all drinking water sources (WHO, 2017).
Types of potable reuse in WHO guidance
- Indirect potable water reuse is defined as the planned addition of treated wastewater into water bodies, as environmental buffers, that are used as sources of drinking water upon additional treatment (e.g., rivers, lakes, reservoirs and aquifers).
- Direct potable water reuse is defined as the introduction of treated wastewater (with or without being retained in an engineered storage) into drinking water distribution systems directly and without additional treatment. However, it also includes treated wastewater blended with raw water immediately before entering a drinking water treatment plant, and “treated wastewater blended with treated water downstream of a conventional drinking water treatment plant” (WHO, 2017).
Water reuse treatment category/type
The WHO does not assign treated wastewater used for direct or indirect potable water reuse to a category or class of recycled water. The recycled water that meets health-based microbial LRVs, chemical concentration targets and radioactivity targets specified by a national or regional authority is considered safe to drink.
Additional context and definitions
Microbial treatment performance targets are a function of the source water’s pathogen concentration data. Consequently, source waters with greater concentrations of pathogens require higher LRVs than source waters with lower pathogen concentrations. In the absence of pathogen data for the derivation of microbial treatment performance targets, using default pathogen concentrations in the source water for enteric bacteria, viruses and protozoa LRVs is recommended (see Table 5.1 in WHO, 2017). For example, 20,000 PCR Detectable Units (PDU) of norovirus per liter was assumed in their LRV calculation (WHO, 2017). The WHO potable reuse guidelines and the WHO GDWQ highlight multiple technologies used for pathogen removal. These technologies, and their combinations, should be chosen by water suppliers based on their specific context (WHO, 2017; WHO 2022). The chemical concentration targets for known chemical pollutants in drinking water are the same for potable water reuse applications and they are not specified in the WHO potable reuse guidelines (WHO, 2017; WHO, 2022). The concentration of contaminants of emerging concern (CECs), including pharmaceuticals, are typically low and currently do not warrant new guideline concentration targets in the WHO GDWQ or other standards (WHO, 2017; WHO, 2022). When a chemical is identified as a concern and it does not have a guideline target, the WHO guidance on water reuse provides approaches to develop screening concentration targets to identify potential health risks.
Potable water reuse specifications
Summary of WHO's Potable Water Reuse Specifications
| Recycled Water Class/Category (Approved Uses) | Source Water Type | Water Quality Parameter | Specification | Sampling/Monitoring Requirements (Frequency of monitoring; site/ location of sample; quantification methods)a |
|---|---|---|---|---|
| Not specified | Treated wastewater | Enteric bacteria default performance target | 8.5 log-reduction | Not specified |
| Enteric virus default performance targetb | 9.5 log-reduction | |||
| Enteric protozoa default performance targetb | 8.5 log-reduction | |||
| Chemical and radiological parameters | multiple | The chemical concentration targets and radioactivity targets in the 2022 WHO GDWQ are relevant for potable reuse schemes (WHO, personal communication) |
Source = WHO (2017; 2022)
a The parameters do not represent guideline targets; they are meant to help identify combinations of treatment and monitoring requirements to ensure proper water quality.
b Default targets assume the source water is untreated wastewater.
References:
Geneva: WHO. Disability-adjusted life years (DALYs).
Geneva: World Health Organization (WHO). 2017. Potable reuse: Guidance for producing safe drinking-water.
Geneva: WHO. 2022. Guidelines for drinking-water quality: fourth edition incorporating the first and second addenda.
Please contact us at waterreuse@epa.gov if the information on this page needs updating or if this state is updating or planning to update its laws and policies and we have not included that information on the news page.