Everybody benefits from an adequate supply of drinking water. In addition, commercial and recreational boaters benefit from adequate navigation depths; farmers who grow wild rice require stable water levels for crops to thrive; water suppliers are impacted by water levels related to Great Lakes intakes, and surface-groundwater interactions for wells and river intakes; thermoelectric energy providers and industries benefit from stable and adequate water levels for cooling; and beach-goers and coastal property owners benefit from stable water levels and, therefore, beaches.

Individual actions and management decisions can change water quantity. For example, water infrastructure, such as dams and river diversion, can impact available water. The amount of water withdrawn from a source can also impact available water. Policies and regulations can set limits on allowable water use. On the other hand, human actions that influence greenhouse gases can also impact water availability. For example, changing climate regulations can lead to changes in precipitation patterns or temperatures, which can impact water levels.

Metrics that have been used to measure water quantity ecosystem services in the Great Lakes include direct measurements such as rain gauges, remote sensing, monitoring networks and models to measure the available water supply; and indirect measures such as halting erosion due to fluctuating water levels (value per ton of soil erosion, value of the possible benefits obtained through different types of prevention efforts), and the built environment (value of human-made structures impacted by erosion, sedimentation, or flooding).

When water quantities change, this can impact the many benefits people get from water. Some examples include:

• Economic development − water is a necessary input into commercial, industrial, energy, and agricultural production. Water availability impacts the value and growth of these economic sectors.
• Water transportation and navigation − adequate water levels are necessary. At the same time, too much water can cause flooding, which impacts land-based transportation.
• Water transportation and navigation − adequate water levels are necessary. At the same time, too much water can cause flooding, which impacts land-based transportation.
• Property values − fluctuating water levels impact coastal water property values due to erosion causing land loss, structural damage, higher insurance costs, and changing waterfront access.

The value of water in economic sectors can be measured by determining the contribution of water to economic output. The price that water suppliers charge for water can also be an indication of the value of water. Water markets, in which water rights are traded, have also been used to place a monetary value on water. Economists have used the scarcity value of water to determine its value.

Methods that economists use to evaluate the values of sedimentation, erosion, or flood control include revealed preference (hedonic), stated preference (contingent valuation/choice), actual expenditure, and replacement costs.