Hydrologists typically do the following:

• Measure the properties of bodies of water, such as volume and stream flow
• Collect water and soil samples to test for certain properties, such as the pH or pollution levels
• Analyze data on the environmental impacts of pollution, erosion, drought, and other problems
• Research ways to minimize the negative impacts of erosion, sedimentation, or pollution on the environment
• Use computer models to forecast future water supplies, the spread of pollution, floods, and other events
• Evaluate the feasibility of water-related projects, such as hydroelectric power plants, irrigation systems, and wastewater treatment facilities
• Prepare written reports and presentations of their findings

Hydrologists may use remote sensing equipment to collect data. They, or technicians whom they supervise, usually install and maintain this equipment. Hydrologists also use sophisticated computer programs to analyze the data collected. Computer models are often developed by hydrologists to help them understand complex datasets. Hydrologists also use geographic information systems (GIS) and global positioning system (GPS) equipment to do their jobs.

Hydrologists work closely with engineers, scientists, and public officials to study and manage the water supply. For example, they work with policymakers to develop water conservation plans and with biologists to monitor wildlife in order to allow for their water needs.

Most hydrologists specialize in a particular water source or a certain aspect of the water cycle, such as the evaporation of water from lakes and streams. The following are examples of types of hydrologists:

Groundwater hydrologists study the water below the Earth's surface. Most groundwater hydrologists focus on the cleanup of groundwater contaminated by spilled chemicals at a factory, an airport, or a gas station. Some groundwater hydrologists focus on water supply and decide the best locations for wells and the amount of water available for pumping. These hydrologists often give advice about the best places to build waste disposal sites to ensure that groundwater is not contaminated.

Surface water hydrologists study water from aboveground sources such as streams, lakes, and snowpacks. They may predict future water levels by tracking usage and precipitation data to help reservoir managers decide when to release or store water. They also produce flood forecasts and help develop flood management plans.

Work done by hydrologists can sometimes include topics typically associated with atmospheric scientists, including meteorologists. Scientists with an education in hydrology who concentrate their efforts in the area of water quality are environmental scientists and specialists. Some people with a hydrology background become high school teachers or postsecondary teachers.