Diversifying the number of sources in a public drinking water system has positives and negatives. According to one source, approximately 75% of the US public drinking water systems use only one source. However, this percentage will trend in the other direction over the next few decades as regulatory standards become more stringent.
Effective communication with the public will be key because multiple sources introduce higher complexity and uncertainty into drinking water systems. The cost of drinking water will also increase.
Why Diversify
Diversifying the sources of public drinking water can provide a range of benefits.
Improved water quality: Diversifying water sources can ensure a more reliable supply of clean water, reducing the risk of contamination from a single source.
Increased resilience: Having multiple water sources can reduce the impact of droughts, natural disasters, or other disruptions to the water supply.
Better cost management: Diversifying water sources can also help reduce the cost of treating water, as different sources may have different contamination levels and require different treatment methods.
Enhanced public health: By ensuring a reliable and clean water supply, diversification can contribute to improved public health outcomes.
Environmental sustainability: Diversification can also help reduce the strain on a single water source and promote the sustainable use of water resources.
Why Not Diversify
Diversifying water sources has some disadvantages.
Increased complexity: Systems consist of interrelated parts that produce outcomes that the parts acting alone cannot. By definition, complexity increases as systems become more diversified.
Increased cost: Additional infrastructure, technology, reporting, and expertise is required to develop and maintain a diversified water supply system
Increased water quality risks: Each new water source introduces new contamination risks, which may be difficult to manage and control.
Variability of water quality: Source water blending is challenging and often requires additional controls and treatment.
Public resistance: Some members of the public may resist changes in their water supply, especially if they believe the new source is inferior or undesirable.
Legal and regulatory challenges: Regulations are challenging to navigate, particularly when multiple sources are involved.
Growing Environmental Concerns
Per- and polyfluoroalkyl substances (PFAS) are currently the emerging contaminant of concern. However, tens of other” emerging” compounds, such as 1-4 dioxane, have been on the USEPA watch list for decades.
The PFAS standards are in the parts-per-trillion range, which is several orders of magnitude stricter than traditional environmental for other compounds in drinking water. The current trend of more regulation and stricter regulation introduces more complexity and uncertainty in the drinking water supply.
Protecting Water Sources
Protecting source water is an ongoing challenge that requires a collaborative effort between land use (planning and zoning) officials and water utilities. Property rights and economic development are often perceived as blockers to fully protecting water supply sources.
Contamination from residential development, industrial activities, and agriculture contains pollutants like chemicals, pathogens, and fertilizers. In the case of fertilizers, excess phosphorous and nitrogen in drinking water supplies can lead to harmful algal blooms.
Building a Reliable System
Redundancy and reliability are more than having just two of something. Inter-related parts must be joined together. In the case of failure of a redundant component, detection must be high, and switching the other component should be instantaneous. A reliable drinking water system requires careful planning, ongoing maintenance, and a commitment to investment in the face of ever-changing environmental regulations and climate variability.
For example, many of the twenty-five percent of systems with more than one drinking water source are not fully interconnected and are not as reliable as they should be. Many utilities lack the organizational capacity, technology, and investment to operate overly complex systems consistently.
Durham (NC) Example
The City of Durham recently requested that the Nello Teer Quarry and a segment of the
Eno River in Durham County be reclassified to allow the quarry to function as a water supply source.
The North Carolina Division of Water Resources worked with the NC Wildlife Resources
Commission and City of Durham staff to reach an agreement in 2019 regarding the
conditions on water quantity by which the City of Durham would be allowed from the river to recharge the quarry. However, during the four years of regulatory review, the presence of contaminants in groundwater near the quarry from releases of petroleum hydrocarbons and chlorinated solvents associated with historical uses of the area.
The City of Durham spent decades planning to add the former rock quarry as one of its groundwater supplies. The quarry represented a diversified approach that introduced a fourth source to three others that the City owned and operated. The City believes the site will be easy to protect for future generations.
Nevertheless, there were strong voices against the new source. Most of the comments focused on concerns of contamination from the existing chemicals and emerging compounds, such as PFAS, in the stormwater runoff that would enter the new drinking water sources.
After some lengthy debate, the NC Environmental Management Commission approved the plan to add the quarry as a drinking water source. Some of the primary reasons cited included careful planning, the City successfully operating a diversified system, and the new source providing another viable option to protect public health.
Summary
Diversifying the number of sources in a public drinking water system has benefits and challenges. Given the current regulatory environment, it is probable that public drinking water systems with diversified sources will increase. Effective communication with the public will be key because multiple sources introduce higher complexity and uncertainty into drinking water systems.
The following sources were used in support of this article:
Congressional Research Service Report (2018)
Draft documents from CH2M Hill
www.epa.org
Reclassification petition to NCDEQ by the City of Durham
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