Water Demand Analysis

The United States Geological Survey (USGS) publishes county level water use estimates every five years categorizing water usage by land use.  LEAM simulations project changes in total acreage for each land use type, which can be combined with the USGS data to predict future water demand.  In this analysis, water consumption rates were based on the USGS consumption data, the only adjustment needed being for new homes, which are required to meet the provisions of the Energy Policy Act of 1992 for water-consuming fixtures. Therefore, residential water demand was adjusted downward by 28 gallons per day, per capita to account new homes.  Population projections from the Regional Economics Applications Laboratory (REAL) at the University of Illinois were used to estimate the number of households based on population change and the projected average household size in the region during the project timeframe. Total water demand was broken down into three categories, residential, commercial, and agricultural, defined as follows:

Residential  water demand is calculated by dividing the sum of Domestic and Public supply water by the number of households. 

Commercial water demand is calculated by a two-step process: 1. Convert the commercial acreage into building square footage via a conversion factor (in this case 13,126); 2. Divide the sum of Industrial and Public supply water by the total square footage from Step 1. 

Agricultural water demand is calculated by summing the Irrigation and Livestock water and dividing by Agriculture acreage. 

The following diagram captures some of the connections between land-use change and water stock in a region.  Water extraction is divided into several sectors including public supply, domestic, industrial, and agricultural water use.  The figure shows how water demand is related to land use change factors such as changes in household units, commercial/industrial buildings, and agricultural land.

Figure 1:  Water demand model

The 2000 USGS Estimated Water Use Report used as a base for the model provides county level water use statistics by category. These categories include:

Domestic Water: Self supplied water used for all indoor household purposes as drinking, food preparation, bathing, washing clothes and dishes, flushing toilets, and watering lawns and gardens.

Industrial Water: Water used for fabrication, processing, washing, and cooling, and includes such industries as chemical and related products, food, mining, paper and allied products, petroleum refining, and steel.

Irrigation Water: Water that is applied by an irrigation system to assist in the growing of crops and pastures or to maintain vegetative growth in recreational lands such as parks and golf courses. Irrigation includes water that is applied for pre-irrigation, frost protection, chemical application, weed control, field preparation, crop cooling, harvesting, dust suppression, the leaching of salts from the root zone, and water lost in conveyance.

Public-Supply Water: Water withdrawn by public and private water suppliers that furnish water to at least 25 people or have a minimum of 15 connections. Public suppliers provide water for a variety of uses, such as domestic, commercial, industrial, thermoelectric power, and public water use.  

Livestock Water: Water for livestock watering, feedlots, dairy operations, and other on-farm needs. Types of livestock include dairy cows and heifers, beef cattle and calves, sheep and lambs, goats, hogs and pigs, horses and poultry.

Sample Analysis (McHenry County)

The reference scenario results are used as a baseline for comparison of the impacts of the different policy interventions (scenarios) on water demand in McHenry County.  As described in the introduction to this section (here), there are three demand sectors:  residential, commercial and agricultural.  Inevitably, residential demand changes are the most dynamic of the demand sectors due to a greater degree of change in residential development than commercial and an almost certain net loss of agricultural land throughout most regions.  Below are the results for the LEAM water demand analysis for the reference scenario in millions of gallons per year.  The table provides the actual water demand data numbers for more detailed analysis.