by Ned W. Paschke, PE, UW-Madison program director in the Department of Engineering Professional Development
Safe and reliable water and wastewater facilities are among the most valuable physical assets in any city.
Drinking water supply and treatment, water distribution networks, sanitary sewer systems, and wastewater treatment/water reclamation plants have helped public health and the environment tremendously, and are often listed among society’s greatest engineering achievements.
Much of this infrastructure is physically buried or otherwise hidden from view. To the general public, it may be almost invisible. When any significant failure takes place, however, the importance of clean water supplies and reliable wastewater service quickly becomes very evident. Drinking water quality problems, service outages, wastewater overflows, or emergency repairs can become costly, harmful, and disruptive for the utilities, customers, and overall community.
The following questions and answers provide an introduction to the public water supply industry in the United States, and a discussion of key aspects of this important service.
1. Who owns and operates the public water systems in the U.S.?
Water is a very decentralized industry in the U.S. Tens of thousands of individual municipalities, utilities, and water districts, large and small, own and operate their own systems. Most of these are public entities, but some are investor-owned water companies. Some large municipal water systems provide water to many millions of people, while some small systems may serve as few as 25 people. In most cases, each utility is responsible for owning, operating, maintaining, managing, and financing its own system. In some cases, a water utility may contract its operations and maintenance functions to a third party. Some water systems also purchase water wholesale from neighboring systems, and then distribute it to their local customers.
2. Where does our drinking water supply come from?
Roughly 63% of the total source water (also called “raw water”) for public water systems in the United States is withdrawn from surface water supplies (such as lakes, rivers, or streams). For example, Chicago draws its source water from Lake Michigan; Washington, D.C. draws its source water from the Potomac River; Minneapolis draws its source water from the Mississippi River, and Denver draws its source water from streams fed by mountain snowmelt.
Overall in the U.S., there are about 53,000 public water systems that provide water service on a year-round basis, including about 41,000 groundwater systems and about 12,000 surface water systems. Since the largest systems tend to be the surface water systems, far more people in the U.S. are served by surface water than by groundwater.
3. What about the water-scarce regions of the country, and cities not located near acceptable water sources – where do they get their water?
Some cities in water-scarce regions “import” a significant portion of their water via long aqueducts. Southern California, for example, relies on several major aqueduct systems, hundreds of miles in length, from Northern California, from the Colorado River, and from the Sierra Nevada mountains. Water conservation practices, reuse of treated wastewater, and desalination of seawater are also becoming increasingly important as supplemental water sources for water-scare regions. Some other cities, though not in dry areas, may still import their water from great distances to reach better quality water sources. For example, New York City draws much of its source water through a system of long aqueducts coming from high quality source waters in the Catskill Mountains in upstate New York.
4. What does a typical water utility do with the water?
Three principal functions of a water utility typically include withdrawal of raw water from a surface water or groundwater source, treatment of this raw water to produce safe drinking water (also called “finished water” or “potable water”) that meets national standards, and distribution of the treated drinking water to customers throughout its service area through a network of pipes, booster pumping stations, and reservoirs. Another significant function of a typical water utility is to provide water of sufficient quantity and pressure so that it can be used for fire fighting emergencies. Since fire fighting requires an intense use of water for a short time, the actual sizing of water pipes and reservoirs in many cities is primarily determined by the fire flow requirements.
5. What processes are typically used to treat drinking water?
A. Coagulation. A chemical coagulant such as alum is added to the water, helping suspended contaminants and particles to clump together into “flocs” for easier removal.
B. Clarification (also called sedimentation). The water passes through slow, quiescent chambers allowing the coagulated particles to settle out for removal. A variation on this process is dissolved air flotation, in which air bubbles are introduced to lift the coagulated particles to the surface for removal.
C. Granular media filtration. The water passes through a large filter bed of granular media (typically sand and/or anthracite). As the water passes through, contaminants in the water are adsorbed to the surface of the granular media particles. The media bed must be regularly “backwashed" to remove the contaminant particles and to prevent the filter bed from clogging.
D. Membrane filtration. The water is forced through manufactured membranes with very fine pores. Substantial pressures are needed to drive the water through some membranes. Reverse osmosis can be thought of as an extremely fine version of membrane filtration, capable of removing even dissolved substances. All membranes must be regularly backwashed to prevent clogging and fouling, and to allow for removal of the captured particles.
E. Disinfection. Water is disinfected to kill or inactivate microorganisms such as bacteria and viruses. In the U.S., disinfection is most commonly accomplished by the addition of chlorine, sometimes in combination with ozone, chloramines, or ultraviolet irradiation.
F. Many other treatment processes are also available, and may be included to improve taste, improve dental health, reduce odors, adjust pH, control corrosion, or remove specific contaminants.
6. How is the quality of drinking water regulated in the U.S.?
All public water supplies must meet the detailed requirements set forth by the U.S. Environmental Protection Agency (USEPA). Numerous individual contaminants are regulated, falling within the categories of microorganisms, organic chemicals, inorganic chemicals, radionuclides, disinfectants, and disinfectant byproducts. In addition to the mandatory federal rules, each state may add supplemental requirements, if desired by that state. In most states, the USEPA authorizes a state-level agency (such as a department of natural resources or a department of environmental quality) to monitor all drinking water utilities in that state and to enforce the EPA rules.
7. Are groundwater utilities and surface water utilities similar to each other?
There are some similarities and some differences. Since surface water sources are typically more “open to nature”, they generally have a more direct exposure to microorganisms and natural organic matter in the environment, and thus generally require treatment for these contaminants. Surface water utilities often draw their raw water from central supply intakes, leading to one or more large central treatment plants (commonly called filtration plants). In a few cases, individual high quality protected surface water sources have been exempted from the filtration requirements otherwise mandated by the USEPA. For example, the water supplies for New York City, Portland, San Francisco, and Boston are exempted from filtration (although they still require disinfection).
Groundwater sources typically have less exposure to microorganisms and natural organic matter, but can have higher concentrations of calcium, magnesium, iron, manganese, hydrogen sulfide, arsenic, radium, or other naturally occurring substances in the ground. In some cases these concentrations are low enough that very little treatment is needed, other than disinfection. When treatment is required, it can sometimes be incorporated at each individual well, rather than at a centralized treatment plant.
8. How can a customer know the quality of water provided by his/her local water utility?
Under USEPA rules, all water utilities must produce an annual water quality report, commonly called the “consumer confidence report.” This report is provided to all customers and can also be found on the website of the water utility. The report includes the levels of any detected contaminants, documentation of compliance with drinking water rules, and other information.
9. How much water does a typical person use in the U.S.?
This depends on how we phrase the question. For example, in the U.S., the total use of publicly supplied drinking water per person averages about 157 gallons per person per day – this includes the water used in the residences, businesses, industries, government, institutions, and system leakage within an average city, divided by the population of the city. Note that this discussion does not include water withdrawn for agriculture, power generation, or other uses - those industries use even more water than the public water systems in many states.
Of the total 157 gallons per person per day, a typical resident uses about 50-70 gallons per person per day inside his/her home. Most of this indoor residential water is used for showers, bathing, toilet flushing, clothes washing, etc. - only a small portion is used for actual “drinking”. Water is also used for outdoor residential purposes, such as for lawns and plantings - outdoor uses can be particularly high in dry regions of the country.
10. Why do we use so much water?
Also, due to the long established structure of our cities and sewer systems, large volumes of drinking water are used for conveying waste materials. It is interesting to note that water prices in many other countries are often significantly higher per gallon (or liter), and water use is much lower - perhaps not coincidentally. Of course, there are also other factors for this, including higher population densities, different construction standards, smaller property sizes, and differing cultural habits regarding water use.
11. How much does water “cost” in the U.S.?
Each utility sets its own billing rates, and these rates vary across the country. Billing rates typically include a fixed customer base charge, plus a usage charge that is based on the amount of water used. An effective “composite” rate can be informally calculated, including the effect of both the fixed charges and the usage charges. In many cases, customers receive a combined bill that itemizes their drinking water service and their wastewater (sewer) service, and sometimes other municipal services.
For many residential customers, effective composite bills are in the range of 0.3 to 0.7 cents per gallon for drinking water service, plus 0.4 to 1.0 cent per gallon wastewater service (or a combined rate of 0.7 to 1.7 cents per gallon for drinking water + wastewater service). In most cases, wastewater service tends to be more costly than drinking water service. In some states, water service billing rates must be approved by a state agency, such as a Public Service Commission.
The true value of water is a complex topic affected by many factors, including water shortages, supply/demand, technology, public infrastructure, and regulations. It is also interesting that commercially bottled water products are hundreds of times more expensive (on a per gallon basis) than publicly supplied water!
12. Is water use consistent across the country?
No. Cities in water-scarce regions of the country tend to use more water per person than cities in water-rich regions. For example, as shown on the attached chart, estimated daily water use per person is approximately 230 gallons per person in Nevada, 200 gallons per person in Arizona, and 250 gallons per person in Utah, compared to the average national water use of 157 gallons per person. Other factors influence this also, including the degree of and types of industrial and commercial activity relative to the overall population.
Public System Water Supplied Per Person in the U.S.
13. Is water use increasing in the U.S.?
Actually, most cities in the U.S. have been seeing a decreasing trend in water use per person in recent decades. This trend is due to several factors, including the implementation of lower flow toilets and fixtures in recent decades, specific water conservation ordinances in some cities, increasing awareness of water costs, and voluntary conservation of water as a precious resource. There are obvious advantages to this trend of more efficient use of water per person. There are also some unintended aspects. The actual operating costs for water and sewer agencies (labor, equipment, chemicals, energy, etc.) are still going up. Cities are also facing a new era of major repairs and replacements within their aging water (and sewer) piping systems. Therefore, with capital and operating costs going up, and water use per person going down, the price per gallon is likely to increase considerably in the future. Higher prices for water, in turn, will likely result in further water use reductions per person. Stay tuned.
14. What are the major issues and challenges within public water and wastewater systems today?
There are many current inter-related challenges and opportunities within the water industry, including:
- Repair and replacement of aging infrastructure
- Drinking water quality in distribution systems and premise plumbing
- Water costs and price increases
- Water shortages and water conservation
- Alternative water sources - wastewater reuse and seawater desalination
- Disinfection byproducts from chlorine and other disinfectants
- Reducing phosphorus and nitrogen in land runoff and wastewater effluents
- Recovery of waste products as a beneficial resource
- Controlling wet weather overflows of sewer systems
- Energy conservation and generation in water and wastewater systems
- Aging workforces and transfer of knowledge to new professionals
15. How large is the problem of aging water and wastewater infrastructure in the U.S.?
The USEPA has estimated that more than $600 billion of capital improvements will be needed for aging water and wastewater infrastructure in the U.S. over the next 20 years. Major expansions of our urban areas took place in the latter half of the twentieth century, including the construction of new water and sewer mains to serve the expanding new areas. While there has always been a need for some repairs and upgrades, a larger percentage of our facilities have now become “older”.
And what is Asset Management? An asset management program often includes an assessment of the system’s level of service, and an estimate of the likelihood of failure and the consequences of failure for the key components. This helps the utility to prioritize short and long term capital replacements and upgrades. Due to the vast scale and replacement value of water and wastewater systems (built up over many decades), it is financially impossible to replace or upgrade an entire system at one time.
16. What are the issues related to the recent water quality problems reported in Flint and elsewhere?
The water utility owns and operates the distribution system (including the watermains), but the building owner owns the interior piping and also most of the service pipe (or “lateral”) that connects the public watermain to the building. Although lead has not been allowed for water system piping for decades, some of the older service laterals were constructed of lead, and some of the older interior plumbing systems included lead at their joints. Some water supplies are more corrosive than others, and some water supplies have more potential than others to pick up and transport lead from lead piping.
Under the USEPA’s “Lead and Copper Rule,” water utilities are required to test water for lead and copper levels at a number of individual testing sites at selected homes and buildings in the service area. Between 5 and 100 total testing sites are required, depending on the size of the utility. The testing sites are selected to include buildings that are expected to be most susceptible to lead and copper. If 10% or more of the test sites show lead concentrations higher than 15 parts per billion, an “Action Level” is triggered. This requires the utility to take additional actions, in consultation with the state regulatory agency. These actions may include a public education program, adding or revising corrosion control chemicals to the water supply, or other revised treatment processes for the source water.
If these actions still do not solve the problem, the next step is to physically replace the lead service laterals. Typically, however, the utility is only responsible for the portion of the lateral that runs from the public water main to a shut-off valve usually near the property line. The majority of the lateral - from the shutoff valve to the building - is owned by the building owner. The water utility may decide to offer partial financial assistance for replacing the building owner’s portion, but the building owner still must decide whether or not to have his/her lateral replaced.
Actual corrosion processes in water systems are complex and beyond the scope of this paper. They are affected by the specific water chemistry, microbiology, pipe materials, hydraulics, and storage time within the system.
17. What is Water Reuse?
“Direct reuse” means that a highly treated wastewater effluent is piped directly to an end use, without temporarily residing in an environmental buffer. In almost all cases, “direct reuse” is only for non-potable, non-drinking water use. Examples include golf course watering, irrigation, industrial cooling water, non-potable wash-water, etc. Although wastewater can be treated highly enough for direct use as drinking water, in practice this is very seldom done (at least so far). In part, there is still a psychological factor involved; many people, even if they know the water was highly treated to drinking water standards, may be less willing to drink that water if it was piped directly from a wastewater treatment/water reclamation plant. This attitude may change over time, depending on water supply vs. demand and public education regarding water reuse. Stay tuned.
18. Is water and wastewater an energy-intensive industry?
Yes. Several thousand kilowatt-hours are typically required for each million gallons of water treated and pumped. Energy is often the 2nd or 3rd largest component in the operating budget of a water or wastewater utility. In many cities, water and wastewater utilities are among the largest individual customers of the local electric company.
For drinking water systems, the largest energy use is typically in pumping; this is affected by the volume of water pumped, the required lift from the groundwater or surface water source, the degree of treatment needed, the elevation differences within the service area, the amount of storage and leakage in the distribution system, the condition of the distribution piping network, and the desired pressures at the customer’s tap.
For wastewater / water reclamation systems, the largest energy use is typically in the biological treatment processes, particularly in aeration. Energy use is also affected by the strength of the raw wastewater, the biological treatment process selected, the amount of pumping required, and the degree to which methane is recovered from the plant’s biosolids digestion processes.
While energy reduction should not be pursued at the expense of reliability, most water and wastewater operations have significant opportunities to reduce energy usage without negatively affecting performance. In fact, many energy conservation practices can actually improve system reliability and reduce down-time.
19. Where can I go for more information about water, water systems, and water quality?
- Local water utilities, including their annual Consumer Confidence Reports
- State agencies, such as departments of natural resources, departments of environmental quality, etc.
- The USEPA
- Professional societies, such as the American Waterworks Association, the Water Environment Federation, and the American Society of Civil Engineers
- Universities and technical colleges
For more information, or to discuss water issues of interest, contact:
Ned W. Paschke, PE, DEE
University of Wisconsin-Madison
ned.paschke@wisc.edu
608-263-4705
608-576-0656 mobile