Drinking Water Violations and Student Test Scores

Racial disparities in student test scores have narrowed since the 1970s, but the average Black American still scores below 75 percent of the average white American on almost every standardized test, according to the Brookings Institution. As education has been shown to increase an individual's income, job stability, and social mobility, understanding ways to reduce racial disparities in test scores may go a long way to decreasing overall inequality in the United States.

Therefore, it is important to understand disparities in inputs into the education production function and to quantify their impact on student achievement. One important disparity that has received relatively little attention is differential exposure to pollution, which can harm health, lead to school absences, and reduce concentration during school. For example, health-based drinking water violations affect about 1 in 12 Americans each year, with disproportionate exposure among disadvantaged households.

A variety of factors influence student test scores, including school-related inputs, such as class size, tutoring, and teacher quality (Guryan et al. 2023, Chetty et al. 2011, Krueger 1999), as well as other factors, such as families and peers (Carrell et al. 2018) and nutrition (Ruffini 2022, Anderson et al. 2018). Even environmental factors, such as air pollution and heat, affect academic performance (Park et al. 2020, Zivin et al. 2020, Ebenstein et al. 2016). Yet, we know relatively little about the role of water quality.

While estimated 16.4 million cases of acute gastroenteritis each year in the US are attributed to contamination in community water systems (Messner et al. 2006), more subtle impacts of water contamination likely go unmeasured in traditional health data. For example, symptoms such as nausea and stomach cramps may not be severe enough to warrant a visit to the hospital or absence from school but could still meaningfully reduce concentration or comprehension of material during school and lead to lower test scores.

Vanderbilt's Approach:

Ongoing research by Michelle Marcus, assistant professor of economics at Vanderbilt University, considers whether drinking water quality is an important input into the education production function by providing the first estimates of the contemporaneous effect of drinking water quality violations on test scores in a modern US context. She exploits plausibly exogenous variation in the timing of water quality violations to estimate the within-student impacts of poor water quality on student test scores. To do so, she combines student-level test score data with geocoded student residential addresses from the North Carolina Research Data Center with detailed geographic information on community water system service areas and drinking water quality violations. She finds exposure to a monthly coilform bacteria violation during the school year decreases math scores by about 3.7 percent of a standard deviation, which is very similar in magnitude to the effect of air pollution on math test scores.