TDS Article - Brent Stewart - Applications Engineer

TDS or 'Total Dissolved Solids' is a measure of the amount of salts or dissolved ions in water. It is the weight of remaining salts after the water has been filtered (water softeners) and the water evaporated, measured in mg/l which is equivalent to ppm or parts per million. Recall chemically, salt is composed of ionic compounds, both positive and negative ions creating a neutral product (no net charge). As a rough rule multiplying the conductivity by 0.65 is approximately equal to the TDS. Conductivity measures a current passed through the water, the higher the TDS or ions in the water, the more conductive. The TDS varies from 50-45,000 ppm depending on the water source.

Standard seawater is 36,000 ppm, depending on the region, higher TDS levels are seen in the Persian Gulf (up to 45,000 ppm). As a rule of thumb, 10 PSI per 1,000 ppm of TDS contributes 10 PSI of osmotic pressure. Therefore the higher the TDS, the higher pressure to required to overcome the osmotic pressure, hence the name Reverse Osmosis.

Reverse Osmosis removes dissolved ions (salts), rejection is 99%+ depending on the membrane and specific ions. The WHO guideline or drinking water standard is 500 ppm.

Pure Aqua, Inc. specializes in RO/NF technology, to see Pure Aqua's standard line of packaged RO equipment visit our website: http://www.pure-aqua.com/reverse-osmosis-systems.html.