Total Dissolved Solids (TDS) in water are primarily caused by the dissolution of inorganic salts and small amounts of organic matter from both natural environmental features and various human activities.
Understanding Total Dissolved Solids (TDS)
TDS refers to the total concentration of all dissolved substances in water, which can include minerals, salts, metals, and some organic materials. These substances are typically in an ionic state (e.g., calcium, magnesium, sodium, potassium, chlorides, bicarbonates, sulfates), but can also include non-ionic molecules. While some dissolved solids are essential for health, high levels can impact water taste, aesthetic quality, and even plumbing systems.
Primary Sources of TDS in Water
The presence of TDS in water is a result of a combination of geological factors and human interactions with the environment.
Natural Environmental Features
Naturally occurring geological processes are a significant contributor to TDS levels in water bodies. As water moves through the environment, it dissolves minerals and salts from the surrounding soil and rock formations.
- Mineral Springs: Water emerging from mineral springs often has high TDS due due to its long contact time with mineral-rich rocks deep within the Earth.
- Carbonate Deposits: Areas rich in limestone or dolomite (carbonate rocks) contribute significantly to TDS, as water dissolves calcium and magnesium carbonates, forming bicarbonates.
- Salt Deposits: Natural underground salt deposits, such as those found in ancient sea beds, can leach into groundwater and surface water, leading to elevated sodium and chloride levels.
- Seawater Intrusion: In coastal areas, the encroachment of saltwater into freshwater aquifers can dramatically increase TDS, as seawater naturally has a high concentration of dissolved salts.
- Erosion and Runoff: Rain and melting snow naturally dissolve minerals from rocks and soil as they flow over land and percolate through the ground, carrying these dissolved solids into rivers, lakes, and groundwater.
Human-Made Activities and Anthropogenic Sources
Human activities also play a substantial role in increasing TDS concentrations, often introducing substances not naturally found in high quantities.
- Road De-icing and Anti-skid Materials: In colder climates, salts (like sodium chloride and calcium chloride) used to de-ice roads and anti-skid materials can wash into nearby water sources, significantly raising TDS levels.
- Agricultural Runoff: Fertilizers and pesticides used in agriculture contain various salts and minerals. When rainwater or irrigation water flows over farm fields, it picks up these dissolved substances and carries them into surface and groundwater.
- Drinking Water Treatment Chemicals: Chemicals used in municipal water treatment processes (e.g., coagulants, disinfectants) can contribute minor amounts of dissolved solids to the treated water.
- Stormwater Runoff: Urban stormwater runoff often carries pollutants from impervious surfaces (roads, parking lots, roofs), including dissolved chemicals, metals, and salts, into drainage systems and natural water bodies.
- Industrial Discharges: Wastewater from industrial processes can contain a wide array of dissolved minerals, salts, and organic compounds, depending on the type of industry.
- Sewage and Septic Systems: Treated or untreated wastewater from residential and commercial properties contains dissolved organic and inorganic materials.
- Household Plumbing and Appliances: Water can dissolve minerals from pipes (e.g., copper, lead, iron) and water heaters as it passes through household plumbing systems.
Common Sources of TDS
Here's a breakdown of common TDS sources:
| Source Category | Specific Examples |
|---|---|
| Natural | Mineral springs, carbonate deposits (limestone, dolomite), natural salt deposits, seawater intrusion, general rock and soil erosion, volcanic activity. |
| Human-Made | Salts used for road de-icing and anti-skid materials, agricultural fertilizers and pesticides, drinking water treatment chemicals, industrial wastewater discharges, sewage effluent, urban stormwater runoff, residential plumbing (dissolved metals from pipes), landfills. |
For more detailed information on water quality parameters, you can consult resources from the U.S. Environmental Protection Agency (EPA) or the World Health Organization (WHO).
