Portfolio Solutions for Safe Drinking Water – Multiple Barriers

by Jay Lund


Only some parts of the world have safe drinking water almost ubiquitously, and only in the last century.  (We lucky few!)  In these countries, drinking water safety relies on a complex portfolio of actions and accountability by individuals, industries, and diverse layered units of government.  The provision of safe drinking water is another example of portfolio approaches to water management.

Safe drinking water usually occurs through a so-called “multiple barriers” approach, an effective way to structure actions when failures have especially dire consequences.  A multiple barriers approach attacks water contamination at several points between water sources and water users.  Because no single barrier to contamination is perfect, erecting multiple barriers can increase the stability and reliability of drinking water safety at a lower cost.

Table 1: Multiple barriers to waterborne diseases

Multiple-barriers Infrastructure Multiple Accountability
1. Banned/regulated chemicals and activities Local water utility, elected boards
2. Source protection: Rivers, lakes, reservoirs, groundwater Public health agencies
3. Drinking water treatment State regulators
4. Distribution system Federal regulators
5. Public health system Professional societies
Universities, NGOs, media

The left column of Table 1 lists common layers of barriers to prevent drinking water contamination. These wide-ranging activities include:

  1. Banning and regulating risky chemicals and activities. These barriers suppress or regulate potential contaminants in the entire economy and watershed, making them less available to enter drinking water systems.  Some chemicals are banned (e.g., DDT ) from the economy and some are limited or regulated (some pesticides, lead, arsenic, and SO2 air emissions) so they are less likely to exist or escape into watersheds and water sources.
  2. Water source protection. These activities focus on reducing the availability and frequency of contaminants in streams, reservoirs, and groundwater which supply a drinking water system.  These can include upstream wastewater treatment, septic system regulations, erosion management, and managing lake and stream water quality to help keep contaminants from arriving at drinking water system intakes.
  3. Treatment of water entering drinking water infrastructure. Drinking water treatment often includes several layers of treatment from settling (and enhanced settling), filtration (sometimes through several filter types and layers), and one or more forms of water disinfection.
  4. Distribution system. These barriers prevent new contaminants from entering the water distribution system by maintaining positive pipeline pressures, regulating cross-connections, and other measures.  In addition, a residual disinfectant (usually chlorine-based, sometimes with disinfection boosters in large distribution networks) is usually maintained to attack any surviving or entering pathogens in the water distribution system.  Local flushing also is sometimes used to reduce residence times of treated water in parts of the distribution systems.
  5. Public health system. If previous barriers fail, it is important to have a public health system which responds with additional public actions to ensure public safety, such as through the utility and public health officials issuing warnings for vulnerable populations, restrictions on particular water uses, or “boil water” orders for some types of contaminants.  In addition, the professional public health system detects any waterborne disease and investigates to find and correct its origins.  The public health system also can organize and apply medical treatment of any illness not prevented by the drinking water system.

Contaminants often have different properties and likelihoods of being introduced into different water system parts, having managing multiple barriers is more likely to intercept contaminants.  Also, not all contaminants are known and it is usually impossible to monitor for all possible contaminants in a timely way. Overall, having multiple barriers increases general water purity and safety.

Barriers for drinking water safety have advanced tremendously.  From ancient times until the 19th century, only selecting better-quality source water, preventing contamination of stored water, and boiling water just before use were widely available to protect drinking water (Frontinus 97 AD).  Only in recent times have new technologies and institutions greatly improved and diversified contamination barriers for drinking water safety (Tarr 1984; McGuire 1999).

A second side of multiple barrier approaches is the multiple layers and paths of accountability for drinking water safety, summarized in the second column of Table 1.  People and institutions are imperfectly reliable, so having multiple layers of institutions and people, often with interacting legal responsibilities and authorities improves overall system safety.  The result is a diverse and mutually-reinforcing ecosystem of institutions and people with means and responsibilities for drinking water safety.  These groups of people span several levels of government as well as professional groups without official drinking water responsibilities.

In most US states, drinking water safety rests first on local water utilities (mostly with locally-elected governing boards).  Local water utility management is directly accountable to water users for reliability, quality, and cost.  But some aspects of safety are poorly suited for local accountability (such as water toxicity or pathogens not related to water taste, odor, or color) – so state regulators (California’s SWRCB) become responsible for setting state standards, secondary inspections, and follow-up regulation and enforcement of state and federal standards.  State regulators, in turn, are overseen by federal regulators (USEPA) who set and can ultimately enforce national drinking water standards for quality, testing, and reliability.  This system of federal regulation delegated partially and supplemented by state regulators is a feature of the US Safe Drinking Water Act.  Both state and federal regulators ultimately also report to independently-elected officials, accountable to the public.

If these direct hierarchical legal water authorities prove insufficient, a separate hierarchy of local, state, and national public health authorities and professionals can come to bear.  These include local and state health departments, and federal public health and disease control agencies.  These public health authorities report to many of the same elected officials, but can act independently, providing an additional path to water system problem identification, accountability, and action.

If this second set of governmental paths of accountability is insufficient, several unelected professional groups and organizations also sometimes become involved in drinking water safety.  These include water quality-related and medical practitioners and their professional societies, including environmental engineers, science, and health professionals in private and public practice.  In addition, nongovernmental environmental and health organizations, university researchers, and the media also sometimes become involved.  In addition to investigating potential waterborne disease outbreaks, these organizations also help develop drinking water safety regulations and standards.  The lead poisoning failures in Flint, Michigan required several of these deeper forms of back-up organizations and individuals to highlight problems neglected by those with governmental responsibilities for drinking water safety.

This diverse portfolio of institutional and personal responsibilities, technologies, and actions has been quite effective.  Most major drinking water safety failures are averted through normal drinking water system utility, standards, inspection, and regulation processes.  But with tens of thousands of water systems nationally, hundreds (even thousands) of problems remain, mostly in smaller rural systems.

Independent testing at each stage, and across stages, with multiple and substantially independent pathways to identifying and correcting problems have greatly improved drinking water safety.  But drinking water system safety is imperfectable and requires vigilance.  Drinking water safety failures can be hard to detect and correct because some contaminants can incur damages and illness for days to years before people become aware of problems.

The complexity of safe drinking water management provides many people with opportunities, interests, and responsibilities for paying attention and acting effectively, especially in a democracy where many ways exist to bring problems to elected officials and the public.  This process continues, even today in California, for some of our most difficult drinking water safety issues.

Further Reading

AWWA Organisms in Water Committee. Committee Report: Microbiological Considerations for Drinking Water Regulation. J. Am. Water Works Assoc. 1987, 79, 81– 88 DOI: 10.1002/j.1551-8833.1987.tb02848.x

Federal-Provincial-Territorial Committee on Drinking Water (2002), From Source to Tap: The multi-barrier approach to safe drinking water, Canadian Council of Ministers of the Environment.

Lund, J. (2019), “Portfolio Solutions for Water – Flood Management,” 3 March, CaliforniaWaterBlog.com

Lund, J. (2019), “Portfolio Solutions for Water Supply,” 10 March, CaliforniaWaterBlog.com

Lund, J. (2019), “Shared interest in universal safe drinking water,” January 13, CaliforniaWaterBlog.com

McGuire, M.J. (2013), The Chlorine Revolution: The History of Water Disinfection and the Fight to Save Lives, American Water Works Association.

Tarr, JA (1984), “Water and wastes: a retrospective assessment of wastewater technology in the United States, 1800-1932,” Technology and Culture 25 (2), 226-263

Summerscales, I.M and E. A. McBean (2011), ”Incorporation of the Multiple Barrier Approach in drinking water risk assessment tools,” Journal of Water and Health  9.2  2011

Marron, E.L., W.A. Mitch, U. von Gunten, and D.L. Sedlak (2019), “A Tale of Two Treatments: The Multiple Barrier Approach to Removing Chemical Contaminants During Potable Water Reuse,” Chem. Res., 2019, 52 (3), pp 615–622, DOI: 10.1021/acs.accounts.8b00612

White, Gilbert (1966), Alternatives in Water Management, Publication 1408, National Academy of Sciences – National Research Council, Washington, DC, 52pp.

Jay Lund is a Professor of Civil and Environmental Engineering at the University of California, Davis.

This is the third in a series of blog posts on portfolio approached to water management. Flood and water supply management portfolios were summarized previously.


About jaylund

Professor of Civil and Environmental Engineering Director, Center for Watershed Sciences University of California - Davis
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