Total Dissolved Solids | Civil Engineering Optional Notes for UPSC PDF Download

What is Total Dissolved Solids (TDS)

Definition and Importance Total Dissolved Solids (TDS) refer to any minerals, salts, metals, cations, or anions dissolved in water. This includes inorganic salts such as calcium, magnesium, potassium, sodium, bicarbonates, chlorides, and sulfates, along with some organic matter. TDS are critical because they represent the mineral content of the water, which can affect taste, quality, and the health implications of the water.

Sources of TDS TDS in drinking water originate from a variety of sources, including:

• Natural sources: Mineral springs, carbonate deposits, salt deposits, and seawater intrusion.
• Human activities: Road de-icing salts, anti-skid materials, drinking water treatment chemicals, stormwater runoff, agricultural runoff, and industrial discharges.
• Piping and plumbing: The materials used in plumbing can contribute to TDS levels.

Measuring TDS
The TDS concentration is the sum of the positively charged cations and negatively charged anions in the water. The measurement of TDS is a qualitative indicator of the number of dissolved ions but does not provide specifics about the nature or relationships of these ions. TDS tests do not directly indicate specific water quality issues like hardness, taste, odor, corrosiveness, or the presence of trace metals and microbiological contaminants.

Impact of TDS Levels

• Low TDS: Water with very low TDS, like deionized water, may taste flat, be slightly acidic (low pH about 5.5), and potentially cause acidosis with long-term consumption. Such water can also be corrosive to metal piping, leading to elevated metal levels in the water.
• High TDS: Water with very high TDS, such as seawater, tastes salty, can cause dehydration, and is harmful with long-term consumption. Elevated TDS can result in a salty or brackish taste, scale formation, and corrosion of metal piping and appliances, reducing their efficiency and lifespan.

Health Risks and Concerns
While an elevated TDS concentration itself is not a direct health hazard, it can indicate other issues:

• Corrosion: Low TDS water can corrode metal piping, leading to elevated levels of trace metals in the water.
• Salinity and Hardness: High TDS levels can result in salty taste, scale formation, and decreased appliance efficiency.
• Indicator of Contaminants: Elevated TDS may suggest the presence of nitrates, arsenic, aluminum, copper, lead, and other metals that are health hazards.

TDS and Water Quality Monitoring

Conductivity and TDS are related and can be used to monitor water quality changes over time. Typical TDS ranges and their concerns are:

• < 50 mg/L: Potential for corrosion problems.
• 250-500 mg/L: Concerns about hardness, iron, manganese, alkalinity, chloride, sulfate, nitrate, and general salt content.
• > 1000 mg/L: Potential for man-made or saline water impacts.

Classification of Water Based on TDS Levels

• Freshwater: 0 to 1000 mg/L
• Slightly Saline: 1000 to 3000 mg/L
• Moderately Saline: 3000 to 10,000 mg/L
• Very Saline: 10,000 to 35,000 mg/L
• Briny: > 35,000 mg/L

Monitoring TDS levels helps ensure the general quality of the water and provides insights into potential contamination or issues with the water supply.