These questions are based on the Science News (SN) article Drinkability.”

Describe and summarize ideas:

1. Explain the article’s central idea in three sentences or less.

Possible student response: There are a variety of potential drinking water contaminants, as well as methods for eliminating contaminants to purify the water. Overall, U.S. drinking water is heavily regulated and clean, but there are occasional weaknesses in the system. Some contaminants are more difficult to remove using standard water treatment techniques, so developing new technologies is necessary.

2. What are some potential drinking water contaminants?

Possible student response:

Microbes including bacteria and viruses.

By-products of disinfectant chemicals such as chlorine and bromine that are used to kill microbes.

Industrial chemicals including perfluoroalkyl and polyfluoroalkyl substances. PFAS are widely used to make nonstick coatings and firefighting foams.

Arsenic is a toxic element that can naturally occur in groundwater or be released into groundwater through agriculture or mining.

Nitrogen-containing compounds that mainly enter water supplies from fertilizers used in agriculture.

Lead is a toxic heavy metal that can leach out of old pipes, especially if corrosive water is sent through those pipes.

3. How many U.S. residents were served by drinking water systems that violated Environmental Protection Agency (EPA) standards in 2015?

Possible student response: EPA records suggest that 21 million people were served by drinking water systems that didn’t meet standards in 2015.

4. How many U.S. residents obtain their water via lead pipes? How can communities prevent the lead leaching from pipes and contaminating drinking water?

Possible student response: Approximately 15 million to 22 million U.S. residents obtain their water via lead pipes. Communities can prevent lead leaching into drinking water by replacing lead service lines or by adjusting water chemistry to minimize leaching.

5. What percent of U.S. residents get their drinking water from private wells instead of public water systems? What contaminant is of particular concern when consuming well water?

Possible student response: About 14 percent of U.S. residents get their drinking water from private wells and other private sources that are not regulated by the Safe Drinking Water Act. Arsenic, a contaminant in ground water, is a concern for people who draw drinking water from wells.

6. What are some existing methods of purifying drinking water from private wells?

Possible student response: Filters remove most but not all contaminants. Some people use expensive reverse osmosis systems.

7. List the existing methods of public drinking water purification discussed in the article.

Possible student response:

Flocculation systems use chemicals called coagulants, shaking and spinning, and filters to remove sediments and other particles from drinking water. Other chemical disinfectants or UV light is then used to kill microbes in the water before it is distributed to homes.

Chemicals can be added to trigger reactions that break down organic molecules into nontoxic forms.

Ion-exchange systems separate contaminants by their electric charge. Such systems can remove ions like magnesium or calcium, heavy metals like lead and arsenic, and nitrates.

Reverse osmosis removes almost everything from water by forcing water molecules through a membrane with extremely tiny holes. Reverse osmosis can replace many other water purification methods but is expensive.

8. What are some new methods of purifying drinking water?

Possible student response:

Ferrate, when added to water, inactivates bacteria, breaks down large carbon-based chemical contaminants into smaller nontoxic molecules and makes ions like magnesium less soluble in water so they are easier to filter out.

Electrochemical membranes made of titanium oxide or titanium dioxide filter water and act as an electrode. The electrode splits water molecules, generating reactive ions that can oxidize and break down contaminants in the water.

A combination of specialized filters, sulfite and UV light is a potentially new way to eliminate PFAS from drinking water.

Read and analyze the graph “New rules boost violations:” 

9. In the graph “New rules boost violations,” what information is displayed on the x-axis and the y-axis?

Possible student response: The y-axis represents the number of water-quality violations in U.S. water systems. The x-axis represents the year from 1980 to 2015.

10. What do the different lines represent in the graph?

Possible student response: The dotted lines represent water-quality violations due to (a) bacteria, (b) nitrate, parasites and viruses and (c) disinfecting by-products, PFAS and other molecules. The solid blue line represents the total number of violations due to all of those contaminants.

11. When have total water-quality violations spiked over time, and why might those spikes have occurred? What do the vertical lines with an asterisk represent?

Possible student response: Water-quality violations appear to have spiked in 1984, 1994, 2005 and around 2015. The spikes occurred close to when new, more stringent rules for water quality were implemented, as shown on the graph by vertical lines with asterisks. Presumably, levels of certain contaminants had been present all along, but only qualified as violations once the new rules went into effect.

12. What types of contaminants did the 1990, 1993, 2002 and 2013 rules likely cover? Hint: Refer to the vertical lines with asterisks for those years and look at the trends in data for different contaminants.

Possible student response: The 1990 rule probably covered bacteria and nitrates, parasites and viruses. Violations for both of those categories increased significantly after 1990. The 2002 and 2013 rules probably covered disinfecting by-products, PFAS and other molecules.

Think critically and discuss:

13. What would you like to see happen to the U.S. drinking water system based on the information presented in the Science News article?

Possible student response: More extensive government testing of public and private water sources for all contaminants, more research on the health effects of chemicals that could contaminate drinking water, stricter regulations to keep drinking water clean for everyone and more enforcement of such regulations.

14. What student research projects related to this article could potentially be conducted?

Possible student response: I could measure the concentrations of various contaminants in water from different sources, develop more efficient and less expensive assays for detecting drinking water contaminants or develop and test more efficient and less expensive methods to remove contaminants from drinking water.