What Are Total Dissolved Solids?
Where Do Dissolved Solids Come From?
Why Should You Measure the TDS Level in Your Water?
The EPA Secondary Regulations advise a maximum contamination level (MCL) of 500mg/liter (500 parts per million (ppm)) for TDS. Numerous water supplies exceed this level. When TDS levels exceed 1000mg/L it is generally considered unfit for human consumption. A high level of TDS is an indicator of potential concerns, and warrants further investigation. Most often, high levels of TDS are caused by the presence of potassium, chlorides and sodium. These ions have little or no short-term effects, but toxic ions (lead arsenic, cadmium, nitrate and others) may also be dissolved in the water.
Even the best water purification systems on the market require monitoring for TDS to ensure the filters and/or membranes are effectively removing unwanted particles and bacteria from your water.
How can water with high TDS be undesirable or harmful?
Why is it especially important for children to consume pure water?
What should the TDS level of my water be?
There is no specific level nor 'good or bad' answer to this question. Generally speaking, for drinking water, a lower level of TDS (purer water) is preferred. The U.S. EPA, all U.S. states, the World Health Organization (WHO) and most nations put maximum limitations on TDS allowed in drinking water. These limitations are typically 500 or 1000 ppm, but they do vary. There is no known minimum for drinking water.
Besides drinking water, a TDS level is specific for each application and particular usage. Though humans generally prefer purer water for their health, fish and plants, for example, require water with widely varying TDS levels, most of which are higher than healthy human drinking water. If you are using a meter to test the water pertaining to a particular device, object or operation, contact the manufacturer of that object. For example, if you are using the meter to test the efficacy of a water filtration system, contact the manufacturer of that system for preferred TDS levels. If you are testing the water for a pool, plants, fish, etc. contact a specialist for your specific application, or the manufacturer of additives or nutrients.
How Do You Reduce or Remove the TDS in Your Water?
Common water filter and water purification systems:
Carbon filtration - Charcoal, a form of carbon with a high surface area, adsorbs (or sticks to) many compounds, including some toxic compounds.
Reverse osmosis (R.O.) - Reverse osmosis works by forcing water under great pressure against a semi-permeable membrane that allows water molecules to pass through while excluding most contaminants.
Distillation - Distillation involves boiling the water to produce water vapor. The water vapor then rises to a cooled surface where it can condense back into a liquid and be collected.
Deionization (DI) - Water is passed between a positive electrode and a negative electrode. Ion selective membranes allow the positive ions to separate from the water toward the negative electrode and the negative ions toward the positive electrode. High purity de-ionized water results. The water is usually passed through a reverse osmosis unit first to remove nonionic organic contaminants.
Total Dissolved Solids (TDS) are the total amount of mobile charged ions, including minerals, salts or metals dissolved in a given volume of water, expressed in units of mg per unit volume of water (mg/L), also referred to as parts per million (ppm). TDS is directly related to the purity of water and the quality of water purification systems and affects everything that consumes, lives in, or uses water, whether organic or inorganic, whether for better or for worse.
*Chart values represent national U.S. averages. Actual TDS levels for geographic regions within the U.S. and other countries may vary.
Click here for the U.S. EPA's list of National Secondary Drinking Water Regulations.
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