The increasing use of home testing devices has made many people newly aware of parts per million (PPM), the standard measure for the concentration of Total Dissolved Solids (TDS). Consumers frequently use a handheld TDS meter to get a quick reading of the water coming from their tap or purification system. Understanding what this number represents is the first step in assessing the overall quality of your drinking water.
Understanding Total Dissolved Solids
Total Dissolved Solids (TDS) represents the combined weight of all organic and inorganic substances dissolved in a specific volume of water. These solids originate from various natural and human-made sources, including naturally occurring minerals like salts, calcium, and magnesium. TDS levels also incorporate inorganic compounds from industrial wastewater, agricultural runoff, and urban drainage, as well as organic matter like decaying plant material.
The concentration is measured in milligrams per liter (mg/L), which is numerically equivalent to parts per million (PPM) displayed on most consumer meters. TDS provides a general indicator of the total amount of material dissolved in the liquid.
Recommended PPM Ranges for Drinking Water
The question of what constitutes a “good” PPM level for drinking water involves both regulatory guidelines and aesthetic preferences. The U.S. Environmental Protection Agency (EPA) has established a secondary maximum contaminant level (SMCL) for TDS, set at 500 PPM. This standard is a guideline intended to manage the aesthetic qualities of public drinking water, not a strictly enforceable health-based limit.
Water exceeding the 500 PPM level may have a noticeable taste, odor, or appearance that discourages public acceptance. The EPA’s guideline for TDS is found within the National Secondary Drinking Water Regulations. This regulatory framework addresses non-health-threatening contaminants that affect the public perception of water quality.
For optimal palatability, most experts suggest a narrower range well below the EPA’s secondary limit. Water with TDS concentrations between 50 PPM and 150 PPM is often considered the “sweet spot” for taste and is sometimes referred to as the gold standard. Water in the 150 PPM to 300 PPM range is generally deemed acceptable, though some may begin to notice a slightly saltier or metallic flavor. Once concentrations climb above 300 PPM, the taste is often described as fair to poor, which is why many consumers seek to reduce their water’s TDS.
Analyzing the Composition of Dissolved Solids
A primary point in water quality assessment is understanding that the composition of the dissolved solids is far more informative than the total quantity alone. A TDS meter only provides a numerical total, meaning it cannot distinguish between beneficial minerals and potentially harmful contaminants. This lack of specificity means a high PPM reading is not automatically dangerous, nor is a low reading guaranteed to be safe.
Beneficial dissolved solids include naturally occurring electrolytes such as calcium, magnesium, and potassium, which contribute to a pleasant taste. Water sources naturally rich in these minerals may have a TDS reading in the upper acceptable range. Conversely, a high TDS reading can also indicate the presence of concerning substances, including heavy metals like lead or arsenic, nitrates, or chemical residues.
Because of this variability, a high TDS reading should be viewed as a signal to conduct a more comprehensive laboratory test that specifically analyzes the water’s chemical makeup. The overall quality of water is determined by the nature of the dissolved substances, not simply their combined mass.
How Filtration Methods Impact PPM Readings
Different water treatment technologies affect the final PPM reading in distinct ways, reflecting their mechanism of contaminant removal. Filtration methods that use a physical barrier to separate water molecules from dissolved ions are highly effective at reducing TDS. Reverse Osmosis (RO) systems, for instance, push water through a semipermeable membrane that blocks most dissolved solids, resulting in a significantly lower PPM.
Water treated by RO or distillation often registers a TDS reading between 10 and 50 PPM. This indicates the water has been stripped of nearly all dissolved inorganic material, including both harmful contaminants and beneficial minerals.
Conversely, activated carbon filters, commonly found in pitcher filters or whole-house systems, operate primarily through adsorption. These systems are excellent at removing specific contaminants like chlorine and volatile organic compounds that affect odor and taste. However, they do not generally remove inorganic salts and minerals, meaning the overall TDS reading often remains largely unchanged. Some modern RO systems also incorporate a final remineralization stage, which intentionally raises the TDS reading to improve the flavor profile.