Finished Drinking Water and Treatment Fundamentals

Drinking water has been called the2ndmost essential human need(after the air we breathe). Every day, over 50,000 community drinking water systems serve over 300 million Americans, with just 3 percent of these systems serving almost 80 percent of the US population.1,2Regulated by thebob体育贴吧安全飲用水法案, and supported by the work of federal, state, tribal and local governments and utilities, the US drinking water system has been recognized as one of the nation’s most significant advances in public health.3

Raw and Finished Drinking Water

About two-thirds of Americans served by community drinking water systems obtain their raw (i.e., untreated) water from surface water sources, such as rivers, lakes and reservoirs.4The remaining third are served by municipal groundwater systems using wells, while some systems use both sources. In addition to source water protection, transforming raw surface water or groundwater into safe and clean (finished) drinking water requires appropriate treatment and ensuring its safe distribution to consumers’ taps through on-site premise plumbing. Without adequate treatment, drinking water consumers are at risk of contracting diseases caused by viruses,bacteria, andprotozoan parasites, as well as the risk of harm from toxic substances.

Drinking Water Treatment Fundamentals

飲用水過濾Conventional water treatment transforms raw surface and groundwater into finished drinking water that is biologically (disinfected) and chemically safe; other treatment objectives include low or no taste or odor, low levels of color and turbidity (cloudiness) and chemical stability (non-scaling and non-corrosive). The critical failure to provide adequate corrosion control was at the core of the highly publicizedlead in drinking waterproblems plaguing Flint, Michigan. Generally, surface water presents a greater treatment challenge than groundwater, which is usually filtered naturally as it percolates through the earth and geological strata. Individual systems customize treatment to address the particular water quality and contamination characteristics of their raw water supply.

Although practices vary from facility to facility, there are four basic processes—as well as finished water distribution and storage—included in conventional surface water treatment and as illustrated in the figure.5

  1. Coagulation and Flocculationhelp remove dirt and other particles through the addition ofalum(or other metal salts) to form coagulated masses calledflocthat attract other particles.
  2. Sedimentationof coagulated, heavy particles through gravity to the bottom of a basin.
  3. Filtration沉澱後的水通過channeling water through sand, gravel, coal, activated carbon, or membranes to remove smaller solid particles not already removed.
  4. Disinfectionby the addition of chlorine destroys or inactivates microorganisms. Additional chlorine may be applied to ensure anadequate residualduring storage or transportation throughout the community.

US Drinking Water System Challenges

Although America’s drinking water remains among the safest in the world, it faces a growing array of increasingly costly challenges—particularly those related toaging infrastructure, including pipe system rehabilitation and drinking water treatment plant upgrades and expansion. Tackling these systemic problems will require realistic priorities andunprecedented collaborationamong all levels of government, utilities and the private sector.

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1President’s Council of Advisors on Science and Technology (2016). REPORT TO THE PRESIDENT: Science and Technology to Ensure the Safety of the Nation’s Drinking Water.

2Roughly 15 percent of Americans, almost 45 million people, get all or part of their water fromprivate wellsand are responsible for monitoring and maintaining the safety of their drinking water.

3National Bureau of Economic Research (2004). The Role of Public Health Improvements in Health Advances: The 20thCentury United States.

4The USGS Water Science School: Public-Supply Water Use.

5Source: Drinking Water Chlorination: A Review of U.S. Disinfection Practices and Issues (2016).