Total Dissolved Solids

Dissoved solids make up 5/100s of one percent of the volume of the Red River.

Total dissolved solids (TDS) is a measure of the total amount of all the materials that are dissolved in water. These materials, both natural and anthropogenic (made by humans), are mainly inorganic solids, with a minor amount of organic material. Depending on the type of water, TDS can vary greatly from a few milligrams per liter to percent levels (tens of thousands of milligrams per liter). Seawater contains 3.5% (35,000 mg/L) TDS. The U.S. Environmental Protection Agency's (EPA) Secondary Drinking Water Standards recommends that the TDS concentrations in drinking water not exceed 0.05% (500 mg/L), based on taste and aesthetics.

TDS in the Red River
TDS levels in the Red River in the Fargo-Moorhead (FM) area are shown in the graph below. While the Red River tends to carry a high suspended-solids loading, as evidenced by turbidity, and the water is considered relatively hard, the dissolved solids content is below the EPA's 500-mg/L guideline for drinking water (red line on graph) even before entering the local water treatment plants.

Graph of TDS (mg/L) for the Red River in the FM metro area for the period July 2001 to April 2003 in relation to the EPA guideline (500 mg/L; red line) for drinking water.

Electrical Conductivity

The Red River contains 1/70th the dissolved minerals found in seawater.

The electrical conductivity of water is directly related to the concentration of dissolved solids in the water. Ions from the dissolved solids in water influence the ability of that water to conduct an electrical current, which can be measured using a conductivity meter. When correlated with laboratory TDS measurements, electrical conductivity can provide an accurate estimate of the TDS concentration. Conductivity measurements for the Red River correlate very closely to the TDS determinations. Water in the Red River is usually below the 900 microsiemens/cm (red line on graph) set for drinking water by EPA's National Secondary Water Standards even before entering the local water treatment plants.

Graph of electrical conductivity (μS/cm) for the Red River in the FM metro area for the period July 2001 to April 2003 in relation to the EPA guideline (900 μS/cm; red line) for drinking water.