AP Environmental Science
Wheeler High School
Mr. Walstead
The Water You Drink
1. How clean do you think your tap water is? Why?
Background
For publicly supplied water, the journey to your tap can be a long one. Water is withdrawn from a natural
source, such as groundwater, a river, or a lake, and treated at a water treatment facility. It is then pumped
into pipes that lead to your indoor taps. At each location on its journey, water may pick up contaminants.
To ensure safe drinking water, the Environmental Protection Agency (EPA) sets water quality standards.
These standards define the maximum amount of different contaminants that can be in public tap water.
More than 90 contaminants are regulated in this way.
The EPA also requires that drinking water suppliers monitor and report on the water quality of the water they
supply. Every year, suppliers that provide water to more than 25 people send out a drinking water quality report.
This report tells consumers where their water comes from and what contaminants were found in it.
Use your local water quality report to answer questions 2 and 3.
2. What natural source or sources supply your local public tap water?
3. Fill in the first three columns of the table below with data from your local water quality report. Calculate
the difference between the average level found and the EPA maximum.
4. List each contaminant from Data Table 1 in column 1. Then use the EPA regulated contaminants list
to fill in the type, potential health effects, and likely source.
5. Why is it important to consider the potential health effects of a contaminant when setting water quality
standards? How might this information affect the maximum contaminant level set by the EPA?
6. If enteric viruses are found in drinking water, what are their likely source and what health effects might
they have? How do you think these viruses could get into the water supply?
7. What chemicals are used to disinfect the water supply? What positive and negative effects can these
chemicals have?
8. Is inorganic chemical pollution primarily the result of natural or human-made factors? Name two
inorganic chemicals and their potential impacts on human health.
9. What role can agriculture play in water contamination? What are the primary causes of agricultural
contamination?
10. What is a dioxin? (see p.302 in the text)? What level of dioxin does the EPA currently allow in drinking
water (MCL)? What is the goal for dioxin levels in drinking water (MCLG)?