Environmental Engineering: Fundamentals and Design - Chapter 10

BOOK TABLE OF CONTENTS
CHAPTER TABLE OF CONTENTS
TOC > Ch. 10 > 10.1 Drinking water quality

# Chapter 10 Drinking Water Treatment

David W. Hand and Qiong Zhang

## Drinking water quality

### Introduction

Our water supply comes from two sources—surface waters, i.e. rivers, lakes and reservoirs and groundwater, which is stored below the earth's surface. Each source presents its own problems. Surface waters often have elevated levels of soil particles and algae, making the water turbid, and may contain pathogens. Groundwater typically has higher levels of dissolved organic matter (yellow color) and minerals such as iron that can cause stains. Both sources may have high levels of calcium and magnesium (hardness) which results in soap scum and scale and both can be contaminated by toxic chemicals.
Algae and aquatic plants in an embayment of Cannonsville Reservoir, part of the New York City water supply system. | Dissolved organic matter (yellow color) in well water from the author's home.

### Regulations

The quality of municipal drinking water supplies is regulated under the Safe Drinking Water Act, passed by Congress in 1974. Under this law, the U.S. Environmental Protection Agency sets Maximum Contaminant Levels (MCLs) for inorganic chemicals such as arsenic, cadmium and mercury and synthetic organic chemicals such as benzene (an industrial chemical), PCBs, atrazine (an herbicide). Municipal drinking water supplies cannot contain any microorganisms which may originate in fecal matter (e.g. Escherichia coli , a species of bacteria found in the guts of humans and other warm blooded animals) because fecal contamination may carry pathogens and spread disease. Recent concerns relating to drinking water include the presence of protozoan pathogens (e.g. Giardia) and the creation of cancer-causing chemicals (trihalomethanes, THMs) when drinking water is chlorinated.

#### Credits

Algae and Aquatic Plants photo: Marty Auer.
Water Flask photo: Emil Groth (Michigan Tech).