Total dissolved solids (TDS) refer to the total concentration of inorganic and organic substances dissolved in water. These dissolved particles are typically microscopic and can include minerals, salts, metals, and organic matter.
Understanding Total Dissolved Solids
Total dissolved solids encompass a variety of components, originating from natural sources like rocks and soil, as well as human activities such as agricultural runoff and wastewater discharge. These can include common inorganic salts and organic matter. Measuring TDS is a general indicator of water quality, important for assessing drinking water purity, maintaining optimal conditions for aquatic life in aquariums, ensuring nutrient balance in hydroponic systems, and preventing scale buildup in appliances and industrial equipment.
Common Methods for Testing Water
Testing water for total dissolved solids is most commonly achieved using a handheld TDS meter, which measures the electrical conductivity of the water. Dissolved ions in water conduct electricity, so a higher conductivity reading indicates a higher concentration of dissolved solids. Before testing, it is recommended to calibrate the TDS meter using a standard solution to ensure accuracy.
To perform a test, obtain a representative water sample in a clean container. Submerge the probe of the TDS meter into the water, ensuring the electrodes are fully immersed but avoiding contact with the container’s bottom or sides. The meter will then display a reading, usually in parts per million (ppm) or milligrams per liter (mg/L), which are equivalent units for TDS measurements. After each use, rinse the probe with distilled or deionized water and dry it to prevent residue buildup, which can affect future readings.
Interpreting Your Test Results
For drinking water, a TDS level between 50 and 150 ppm is considered excellent, suggesting minimal dissolved impurities. Levels between 150 and 300 ppm are considered good, while 300 to 500 ppm are fair, still potable but potentially noticeable in taste. Above 500 ppm, water quality is considered poor for drinking due to potential taste issues or high mineral content.
For specific applications, ideal TDS ranges vary significantly. In hydroponics, nutrient solutions have TDS levels ranging from 500 to 1500 ppm, depending on the plant growth stage and type. Aquariums, particularly freshwater setups, aim for lower TDS levels, below 200 ppm, to mimic natural habitats and reduce stress on aquatic organisms. A high TDS reading does not identify specific contaminants; it could mean high beneficial mineral content or high levels of undesirable substances.
Addressing Variances in Water Quality
If drinking water has high TDS, exceeding 500 ppm, common treatment methods include reverse osmosis (RO) systems or distillation. Reverse osmosis forces water through a semi-permeable membrane, effectively removing a significant percentage of dissolved solids. Distillation involves boiling water and condensing the steam, leaving dissolved impurities behind.
For applications requiring extremely low TDS, such as in laboratories or certain industrial processes, deionization can remove nearly all dissolved ions. If RO or distilled water is used for drinking and a higher mineral content is desired, remineralization filters can reintroduce beneficial minerals, slightly increasing the TDS. In hydroponics, adjusting nutrient concentrations is a primary method for managing TDS levels to meet plant requirements.