What are Total Dissolved Solids (TDS)?
Total Dissolved Solids, or TDS, refers to all the inorganic and organic substances dissolved in water. These substances include minerals, salts, metals, and some organic compounds. The concentration is typically measured in milligrams per liter (mg/L), which is equivalent to parts per million (ppm). A TDS reading of 100 ppm means that for every one million particles in the water, 100 of them are dissolved solids.
Common sources of TDS include natural springs, rocks, and soil, as well as man-made sources like industrial waste, urban runoff, pesticides, and aging infrastructure. Some TDS, such as beneficial minerals like calcium and magnesium, are harmless and can even be desirable. Other forms, like lead, arsenic, or excessive nitrates, can pose serious health risks. Therefore, a TDS reading is more of an indicator of water purity rather than absolute safety.
Understanding what is an unsafe TDS level
While the EPA has not set a mandatory standard for TDS due to its wide range of sources, it has established a secondary standard for aesthetic reasons. The EPA's recommended maximum level for TDS in drinking water is 500 ppm, as levels above this can cause water to have a salty, metallic, or bitter taste, and lead to aesthetic problems like water spots on dishes.
However, a TDS level above 1,000 ppm is generally considered unsafe for human consumption. Water in this range is often corrosive, may contain high levels of harmful substances, and can cause scaling and clogging in pipes and appliances. It's crucial to understand that exceeding the 500 ppm aesthetic limit doesn't automatically mean your water is dangerous, but exceeding the 1,000 ppm limit should be a serious red flag requiring immediate action.
High TDS vs. Unsafe Water: The Critical Difference
A high TDS reading from a simple meter does not distinguish between harmless minerals and toxic contaminants. For example, water flowing through limestone can have a high TDS due to calcium, which is benign. On the other hand, water contaminated by industrial runoff could have a low TDS reading but contain highly toxic substances that a simple meter cannot detect. The critical takeaway is that the TDS reading provides a quantitative measure of total dissolved material, but a qualitative analysis is necessary to determine if an unsafe TDS level is due to hazardous substances.
How to Test Your Water for TDS and Contaminants
Using a TDS meter
A handheld TDS meter is a simple, affordable tool for getting a quick reading of your water's TDS level. It measures the electrical conductivity of the water, which correlates directly with the concentration of dissolved solids. While useful for monitoring changes over time or checking the effectiveness of a filter, it does not reveal the specific makeup of the solids. A TDS reading of 0 ppm, for instance, could mean pure water, or it could mean water contaminated with non-conductive, yet toxic, substances like certain volatile organic compounds (VOCs).
Getting a comprehensive lab analysis
The most reliable way to know what is in your water is to get a professional lab analysis. A certified laboratory can perform a detailed chemical breakdown, identifying specific contaminants like lead, nitrates, pesticides, and other harmful elements. You can often obtain this service through a local water quality authority or a private lab. For an authoritative resource, consult a local water quality guide, such as the Los Angeles Public Library's water quality resources.
Comparison Table: TDS Levels and Interpretation
| TDS Level (ppm) | Water Quality | What it Means |
|---|---|---|
| < 300 | Excellent/Good | Usually has a pleasant, clean taste and contains moderate mineral content. |
| 300 - 500 | Good/Acceptable | Often has a noticeable mineral taste but is generally considered acceptable. (EPA secondary maximum) |
| 500 - 1000 | Poor | Can cause aesthetic problems like an unpleasant taste or odor. Requires further testing. |
| > 1000 | Unsafe | Not recommended for drinking. Requires immediate investigation and filtration. |
| > 2000 | Unacceptable | Potentially corrosive and likely contains very high levels of minerals or other contaminants that may overwhelm household filters. |
Common Sources of High TDS in Tap Water
High TDS readings can result from a variety of factors, both natural and artificial:
- Natural Sources: Water passing through geological formations can pick up minerals and salts, which is a common cause of high TDS in well water.
- Agricultural Runoff: Fertilizers and pesticides used in farming can seep into groundwater, increasing the TDS.
- Industrial Waste: Discharge from industrial plants can introduce heavy metals and other contaminants into the water supply.
- Aging Plumbing: Corroded pipes, especially older lead pipes, can contribute to elevated TDS levels and introduce toxic heavy metals.
- Urban Runoff: Road salts and other chemicals used in urban areas can wash into water sources, elevating TDS.
What to Do About an Unsafe TDS Level
If you receive a high or potentially unsafe TDS reading, follow these steps:
- Stop Drinking the Water: Immediately switch to bottled water or another safe source until you have a clear picture of the contaminants.
- Get a Lab Test: Invest in a comprehensive water analysis from a certified laboratory to identify the specific substances present.
- Consult Experts: Share your lab results with your local water utility or a water treatment professional to understand the risks and your options.
- Consider a Filtration System: If harmful contaminants are identified, consider installing a water filtration system, such as a reverse osmosis system, a distiller, or a specific filter designed to target the identified contaminants.
Conclusion
Understanding what is an unsafe TDS level is an important first step toward ensuring the safety of your drinking water. While a reading above 1,000 ppm is a definitive warning sign, remember that a high TDS is not always a direct indicator of danger, and a low TDS is not a guarantee of safety. The only way to truly know your water's quality is through a professional lab analysis. By taking action and testing your water, you can make informed decisions to protect your health and the health of your family.
