# 3.5: Vocabulary

Difficulty Level: At Grade Created by: CK-12
Body of water
A significant amount of water either naturally (such as lakes, rivers, and oceans) or man-made (such as ponds, lakes, and harbors).
Contaminant
A substance that may be harmful to humans or other forms of life when released into the environment.
Epidemic
a widespread outbreak of a contagious disease.
Gravity
The force of attraction exerted between objects. Often, this is the force of attraction that the earth exerts on objects at its surface.
Pathogen
A disease-producing organism.
pH\begin{align*}pH\end{align*} (potential of Hydrogen)
A measure of the activity of hydrogen ions (H+)\begin{align*}(H^+)\end{align*} in a solution. This is a measure of the solution’s acidity or alkalinity. pH\begin{align*}pH\end{align*} is the logarithm of the reciprocal of the effective hydrogen-ion concentration and is a number between and 14\begin{align*}14\end{align*}; the number has no units. A pH\begin{align*}pH\end{align*} of 7\begin{align*}7\end{align*} indicates neutrality, that is, the solution is neither acidic nor alkaline. pH\begin{align*}pH\end{align*} numbers lower than 7\begin{align*}7\end{align*} indicate acidity, while pH\begin{align*}pH\end{align*} numbers higher than 7\begin{align*}7\end{align*} indicate alkalinity. Each change of 1\begin{align*}1\end{align*} pH\begin{align*}pH\end{align*} represents a tenfold change in acidity or alkalinity.
Pollute
To make something dirty, foul, or unclean.
Potable
Potable water is water that is clean enough to drink.
Precipitation
Water that falls from the atmosphere to the earth’s surface. The most common form of precipitation is rain. Snow, sleet, hail, and freezing rain are also forms of precipitation.

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