Managing water reuse risks

As water reuse becomes an increasingly necessary component of regional and global water sustainability strategies, public and private stakeholders are ramping up investments accordingly. A host of advanced treatment techniques are rapidly increasing the feasibility and safety of reclaimed water in a wide array of applications, spanning irrigation, industrial processes and potable consumption.

However, successful water reuse plans must navigate several factors, including water quality regulations , diverse public perceptions and the instinctive concerns of consuming treated wastewater.

Robust water quality regulations are essential for fostering public trust related to reused water consumption. These regulations, typically tailored to the unique needs of specific regions, dictate permissible levels of a multitude of contaminants in different water classifications, ensuring that each type meets stringent safety standards for its intended use. While the public readily grasps this concept in the context of conventionally treated freshwater for drinking, the acceptance of these standards for treated wastewater faces skepticism.

Among the various water reuse approaches, IPR and DPR are gaining increased attention as viable solutions for augmenting drinking water supplies. However, implementing either of these relatively new techniques requires comprehensive study of contaminants in the water, clearly-defined treatment requirements, extensive public education campaigns - and expansive hydro-geological environmental research in the case of IPR.

IPR encompasses treating wastewater and introducing it into an environmental buffer, such as a groundwater aquifer or surface water reservoir, where it undergoes natural filtration and biodegradation before eventual extraction and treatment for potable use. DPR, on the other hand, entails treating wastewater to drinking water standards and introducing it directly into the drinking water distribution system.

IPR faces less challenges to overcome because of the natural filtration buffers it uses and its successful use over the past decade. However, permitting IPR requires robust regulations for wastewater discharge, along with stringent groundwater management allowing to prevent contamination of the receiving water body. Regions with naturally arid or semi-arid climates - such as Australia, Namibia and parts of the southwestern United States - have successfully integrated IPR plans into their water management strategies, often leveraging existing water recycling infrastructure and the natural filtration capacity of their geological formations.

The absence of an environmental buffer in DPR requires more advanced treatment processes and stringent monitoring to ensure compliance with drinking water standards. Although this method achieves the highest water recovery, DPR frequently faces public opposition because of the psychological challenge associated with drinking water sourced directly from wastewater. To address these concerns, countries like Singapore, Israel, Egypt and the United States - which actively deploy DPR or are developing permitting programs - are implementing rigorous multistep treatment systems, often combining advanced treatment technologies with additional safeguards, like activated carbon filtration.

The regulatory landscape for IPR and DPR is emerging and evolving quickly, reflecting advancements in treatment technologies, new scientific understanding, potential risk awareness and variable levels of public acceptance. Most regulatory frameworks for potable reuse focus on ensuring the safety of finished product water by setting cautious water quality standards, mandating extensive treatment and requiring rigorous monitoring systems. These frameworks address:

• Microbial and chemical contaminants: Regulatory agencies worldwide prioritize the removal of microbial contaminants, such as bacteria and viruses, which pose immediate health risks. They also establish limits for various chemical contaminants, including heavy metals, pesticides, pharmaceuticals and disinfection byproducts - all due to their potential negative long-term health impacts.

• Environmental buffering: Specific to IPR regulations, minimum retention time specifications in the reservoir or aquifer ensure sufficient natural attenuation and biodegradation of contaminants in the discharged treated wastewater. These regulations also address potential impacts on receiving water bodies, ensuring the wastewater does not compromise ecological integrity.

• Treatment technologies: Every regulatory framework for potable reuse must specify a treatment approach to address contaminants specific to the region. This typically calls for a combination of multiple processes, including ultrafiltration, reverse osmosis, ultraviolet disinfection and advanced oxidation, each targeting specific types of impurities.

• Emerging contaminants: Recognizing the limitations of traditional monitoring approaches, many regulatory frameworks are incorporating provisions for monitoring emerging contaminants, such as endocrine disruptors and personal care products, which are not routinely monitored but pose potential risk, even at low concentrations.

• Monitoring and risk management: Rigorous monitoring steps are essential for verifying the effectiveness of treatment processes, identifying off-specification water and ensuring the long-term safety of potable reuse systems. Many regulatory frameworks are incorporating risk management approaches - such as the hazard analysis and critical control points system, a preventative system designed to identify and control potential hazards throughout the water treatment process - to proactively implement preventive measures and maintain safety.

Despite the significant progress in water reuse technology, public health concerns remain at the forefront when implementing any system. As a result, numerous epidemiological studies have been conducted on existing IPR projects, covering a variety of treatment technologies, environmental buffers and blending ratios of recycled water to fresh water sources. To date, none have reported adverse health impacts in the communities served. In fact, the US National Research Council concluded in a 1998 evaluation of IPR that the risks associated with these types of projects were comparable to or even lower than those from conventional water sources.

The safety of IPR stems from a robust multistep treatment approach, comprised of source control, advanced wastewater treatment processes, environmental buffering, potable treatment and rigorous monitoring throughout. IPR monitoring programs typically analyze water for a comprehensive range of characteristics, including microbial indicators, chemical contaminants and process analytical values. The use of chemical indicators and carriers, which represent broader groups of contaminants with similar properties, helps ensure the removal of both known and unidentified compounds.

While international organizations - such as the World Health Organization and the International Water Association - develop best practice guidelines and disseminate scientifically-predicated frameworks for water reuse and sustainability, responsibility lies with national and regional governmental agencies to implement and enforce these structures.

By necessity, IPR and DPR are becoming increasingly common around the world to combat water scarcity, particularly in drought-stricken regions and arid geographies. While IPR is a proven safe and effective cornerstone in many municipal water security master plans, DPR is a newer technology and has challenges to overcome in regard to obtaining the community’s trust.

However, the right treatment technologies are more than capable of purifying wastewater streams for clean drinking water. Effectively implementing these sorts of systems requires diligently researching regional contaminants to properly specify and build treatment systems. Then, outreach, education, open dialogue and transparency are critical to gain public support for these projects.

While both IPR and DPR projects incur economic cost, they help municipalities attain water sufficiency and security to provide safe and continuous supply to the communities they serve. As the global population grows and weather patterns change, these and potentially other treatment techniques will become more necessary to ensure sustainable water yield for generations to come.