Water is essential to life and it is obvious that an adequate supply of clean potable water is essential not only for personal health but also for maintaining a nation's economic well-being.

In the United States, one of the greatest engineering accomplishments of the twentieth century was the development of the nation's water systems. These water systems comprise a number of integrated components:

1. the water supply system, including dams, reservoirs, rivers, aquifer systems and water wells that are the source of our water, and the associated conveyance devices for delivering water where it is needed for domestic, commercial and agricultural uses;
2. the water treatment system, including water treatment plants that remove impurities and harmful agents and which makes water suitable for domestic consumption and other uses; and
3. the water distribution system, comprising networks of pipes, pumps and storage tanks that deliver clean water on demand to homes, commercial establishments and industries.

Beginning about 100 years ago and continuing throughout the twentieth century, cities, states and the federal government made enormous investments in water systems to provide adequate supplies of water for use in the home, industry and agriculture. Significant gains in public health were realized by protecting source waters and installing water treatment plants to provide chemically and microbiologically safe water. These successes are evident by the virtual elimination in the U.S. of the most deadly water-borne diseases including typhoid and cholera.

With the passage of the Safe Drinking Water Act in 1974, efforts to improve the potability of our water supply expanded. Between 1984 and 1998, for example, the Centers for Disease Control (CDC) received reports of at least 12 waterborne cryptosporidiosis outbreaks which had caused an estimated 50 deaths and intestinal illness in more than 400,000 people.(1) In response, the U.S. Environmental Protection Agency (EPA) recently finalized, on January 14, 2002, the Long Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR) designed to improve control of the protozoan Cryptosporidium through more rigorous public water filtration standards.

For a comprehensive look at the current drinking water standards, see the EPA's Office of Water statement.

In summary, today, because of our water supply, treatment and distribution systems, the U.S. enjoys the best drinking water quality of anywhere in the world. This was achieved by unparalleled accomplishments in the integration and development of the components of the nation's water systems.

The Vulnerability of the System

Regardless of improved standards and progress in water safety, with the advent of global terrorism, nations must now question the vulnerability of water systems to deliberate attack or sabotage. Although recognized in the past as a possibility, this vulnerability has not received much attention. Part of the reason is that reported instances of deliberate sabotage of our water supply system are rare, yet there have been some notable examples. In Pittsburgh, Pennsylvania, there was an instance of intentional dispensing of the pesticide chlordane into the distribution system, and in The Dalles, Oregon, a religious cult tried, in 1984, to sicken the town by adding bacteria into the town's water. When that proved unsuccessful, the cult turned to food poisoning and sickened more than 750 persons. Until the anthrax instances in the last six months, this was the only successful act of bioterroism in this country. Other reasons that water security has not received heightened attention until recently is the fact that the development and maintenance of existing water systems receive primary attention.

Another vulnerability of our systems is the reality that many components of U.S. water systems are aging and need repairs, replacements or upgrades. This state of affairs is not new. We have heard repeated concerns about our aging infrastructure. But now, in the context of September 11, we are looking at the infrastructure of our water systems in a new light and thinking about things that must be done to protect our water systems from intentional acts. While driven by a sense of urgency because of recent events, we should not act precipitously. We need to consider carefully what is possible and what can be done with new approaches that ensure both the security of our water systems, while at the same time using such investments to enhance the reliability and capability of such systems. These are things that we should be doing anyway. After all, the fundamental mission of such water systems is to protect human health and insure economic well-being, and we should be asking ourselves whether there are better ways to do that.

Physical Damage of the Water System

What elements of the water system are most vulnerable to physical damage? How do concerns for physical damage vary depending on the source of water? How can we protect water systems from physical damage?

Dams, aqueducts and pumping stations that capture and convey water over long distances are especially vulnerable to physical damage. But even water supplies taken from rivers or lakes may suffer if intakes are damaged. Similarly, groundwater withdrawn from wells relies on pumps and infrastructure delivery. The control of human access to critical water supply system components is an important issue and responses are likely to be much different for water supply systems located in parks and public places versus remote areas.

While steps have been taken in the last twenty years, e.g., fencing and covering reservoirs, more is needed to prevent intentional acts. Some aqueducts are hundreds of miles long; protecting these systems is especially challenging. Water supply systems are designed to withstand natural disasters. In-place systems for natural disaster monitoring and response could serve as platforms to incorporate intrusion sensors and quick response to intentional damage. The distribution system is more difficult to secure; though potentially affecting a smaller population, mass exposure is not needed if the goal is fear and anxiety.

Agents of Contamination

What chemical or biological agents may do the most harm to human health and disrupt the beneficial uses of water? What points in the water supply, water treatment and water distribution system are most vulnerable to release of such agents? What amount of such agents would harm humans or disrupt service?

It is believed for many toxic chemicals that truck-load quantities are needed to cause harm to the water supply system because of the very large volumes of water being handled. But this matter needs thoughtful analysis. Small quantities of toxic chemicals, even if not directly harmful, may cause panic and great economic disruption. Who would want to consume water with intentional addition of low levels of lead or cyanide? Biological agents may be harmful at very low levels. The infective dose for certain spores or protozoan oocysts may be fewer than ten, and thus small volumes of these agents in concentrated form may contaminate very large volumes of unfiltered water. These issues are relevant to both surface water systems and those relying on groundwater as their source, especially those using carbonate or other aquifers in which the water residence times are relatively short. Carbonate aquifers comprise water-bearing strata like limestone and dolomite. Overtime, as these rocks dissolve, channels may form that convey water through the subsurface without the benefit of filtration, as occurs with a sandy aquifer.

Elevated portions of distribution systems are vulnerable to entry of chemical or biological agents because the water may not be under pressure, meaning that a pump is not needed to overcome the system pressure. The distribution system, though pressurized, is especially susceptible to the introduction of an agent because by its very design the system is very accessible. Contaminants could be pumped into the distribution system unless prevented by a back-flow prevention valve. From time to time, there are reports of accidental pumping of solutions into the distribution system. Something added to water does not have to be toxic; merely introducing taste or odor would be very disruptive if the goal is fear and anxiety.

Early Detection

How can we achieve early detection of chemical or biological agents in the water supply system in time to take corrective action before water gets to a water treatment plant or into the distribution system?

We need better monitoring for early warning of the intentional addition of chemical or biological agent to the water supply. Water supplies are monitored routinely for a small number of contaminants and much less frequently for a large number of contaminants. Conventional laboratory methods are time consuming and require skilled analysts. Together, this means that problems arising from intentional acts may not be detected until chemical or biological agents are at the treatment plant, or worse, in the distribution system. Some large U.S. systems, notably that of San Francisco and New York City, have no treatment other than disinfection with chlorine or chloramines. This underscores the need for better monitoring and standby treatment capabilities.

Most analytical equipment is highly automated and could very likely be made more autonomous with new technologies. The chemical industry and some of our national laboratories are developing 'chemical analysis on a chip' for hand-held, portable, chemical analysis systems and 'canary on a chip' for detection of hazardous compounds in the work place. With modification, such systems may be useful in routine monitoring of water supplies for a broad spectrum of compounds, both known and unknown. Innovations in immunoassays and nanotechnologies hold promise for rapid screening of chemical and biological agents. Time-tested methods such as increased chlorine demand, taste and odor, turbidity and other measures are useful surrogate indicators in conjunction with new procedures. For approved current analytical techniques go to the EPA's listing.

The Benefits of Interconnectedness

How can water supply system operations be reconfigured to provide greater interconnectedness among source water supplies and among potable water distribution systems? What might be the potential for groundwater or irrigation water resources to shore up contaminated surface supplies on an emergency basis?

Interconnectedness means that in-place conduits allow the transfer from one water supply system to another. Interconnecting water supply systems offer greater assurance that if one component of the water supply system is lost, then other water supplies may be put online to transfer water through stand-by conduits. Similarly, water distribution systems could be interconnected so that one locality may help another under emergency conditions. These interconnected systems would be designed with appropriate controls to prevent cross-contamination and the spread of unwanted agents.

Mutual aid pacts could include water supply, laboratory resources, operating assistance and repair response. Aside from the technical issues, how this systems approach, often called "regionalization," would work in practice requires cooperation on a regional (often watershed) basis. Historically, because of the fragmented nature of the water supply industry, there has not been as much attention to design for interconnectedness unless prompted after the fact by a chemical spill or natural disaster.

The U.S. has experienced only few deliberate acts of local water supply systems sabotage [e.g., Pittsburgh and The Dalles]. Early detection and mutual aid with alternative water supply being brought allows time for flushing or repairing. Greater interconnectedness results in inherently greater stability and flexibility, as networks more resilient to upset than monolithic systems. In the arid west, separate water supply systems are in place for agriculture and domestic use. Since so much more water is used in agriculture than by municipalities, conceivably interconnecting the agricultural water supply or groundwater systems could augment the domestic supply in an emergency. Again, there are many questions, both technical and institutional, on how this would work.

New Technologies and Strategies

What changes in system operations and what new technologies may provide a safeguard against chemical or biological agents? How may multiple barriers be incorporated in treatment plant operations and in the distribution system to ensure greater safety in our domestic water supply?

As mentioned above, we should think of new ways to supply and treat water. Examples include the installation of robust, stand-by systems that could deal with chemical or biological threats. For example, standby powdered activated carbon treatment and standby ozonation treatment would provide some protection for a spectrum of chemical and biological agents. New technologies and augmented conventional technologies are needed. Fortunately, advances in membrane, sorptive and oxidative technologies can be brought to bear on this problem. Nanofiltration and ultrafiltration can remove higher molecular weight organic compounds and biological agents.

In water reuse, a fundamental design paradigm is to install multiple barriers that provide adequate safeguards in converting wastewater to potable water. Such systems are not dependent on one process but several in a train that provide backup protection. Similarly, we need to extend the multiple barrier concept to create a series of hurdles that guarantee greater assurance that we can cope with chemical and biological agents. These barriers may extend from the water treatment plant to include the distribution system and point of use. Multiple barriers comprising storage capacity, enhanced treatment systems and mutual aid provide the means and time to address a problem.

Preventing Cyber Attack: What Can Be Done

Are our water supply systems vulnerable to cyber attack and what can be done to safeguard against such threats?

Historically, most of the concerns for the safety of the water supply system have focused on natural phenomenon. Not to be overlooked, however, is the realization that essentially every component of the water supply system is highly automated and dependent on electric power. This includes electronic control and provision of electricity for water pumping and storing, water treatment operations and water transmission. Although these operations are backed up by manual controls, great damage could be done if the power to control and pump water, and run treatment systems, were lost for a period of time as a result of cyber or physical attack to the electrical grid. Electronic security and emergency control and power generation backup capabilities of the water supply system need careful analysis and possible re-engineering. This concern could be just as real as chemical or biological threats to the water supply.

Among the items listed, top priority should be given to protect physical structures for water storage that serve large populations and that would be very difficult to replace, and to the maintenance of water quality through better monitoring, new treatments and incorporation of the concept of multiple barriers.

Conclusions

The issues discussed are crosscutting among disciplines and institutions. Answers to these questions and the designs for effective solutions to key problems will require broad-based studies from academic and governmental research institutions, professional organizations, practitioners and commercial operators. The challenges are great but so are the resources to make our water safer than ever before.