Water quality is often gauged by the total concentration of dissolved substances, measured in parts per million (PPM). This PPM value is a direct indicator of Total Dissolved Solids (TDS) present in the water supply. A high PPM reading suggests a greater quantity of non-water material, which can affect the water’s taste, appearance, and how it interacts with plumbing and appliances. Understanding how to manage this measurement is the first step toward improving water quality in a home or commercial setting. The methods for lowering PPM range from highly efficient, comprehensive systems to targeted, localized filtration.
Understanding Total Dissolved Solids
Total Dissolved Solids (TDS) refer to the inorganic salts, minerals, metals, and small amounts of organic matter dissolved in water. These components usually include positively charged ions like calcium, magnesium, sodium, and potassium, and negatively charged ions such as chloride, sulfate, and bicarbonate. While TDS is not typically considered a direct health hazard, it serves as an overall gauge of water purity and affects aesthetic qualities.
High TDS readings can originate naturally, such as water flowing through mineral-rich regions, or from human activities like agricultural runoff and industrial discharge. High concentrations cause scaling in household items like pipes, water heaters, and kettles, shortening their service life. For drinking water, TDS levels above 500 PPM are often associated with objectionable taste and excessive scaling. The ideal range for taste and appliance longevity often falls between 50 and 150 PPM, though water below 50 PPM can sometimes taste “flat” or insipid.
Comprehensive Water Reduction Systems
To achieve the lowest possible PPM readings, comprehensive water reduction systems are employed, including Reverse Osmosis, distillation, and deionization.
Reverse Osmosis (RO)
RO systems use pressure to force water molecules through a semi-permeable membrane, which rejects most dissolved ionic contaminants based on size and electrical charge. A properly functioning residential RO system can remove 95% to 99% of dissolved salts, often resulting in treated water with a TDS reading as low as 10 to 50 PPM. This mechanical separation leaves the unwanted dissolved solids behind in a concentrated waste stream that is flushed to the drain.
Pre-filtration, typically using carbon and sediment filters, is employed to protect the delicate RO membrane from fouling by larger particles and chlorine. This crucial step helps maintain the system’s high rejection rate over time.
Distillation
Distillation offers another pathway to extremely low PPM water by mimicking the natural hydrologic cycle. Water is heated to its boiling point, turning it into pure steam while leaving behind all non-volatile dissolved solids, metals, and minerals in the boiling chamber. The steam is then cooled and condensed back into liquid form, often yielding water with a reading of 0 to 5 PPM.
This method is highly effective at removing inorganic solids, but it is typically slower and more energy-intensive than RO, making it less practical for high-volume residential use. Furthermore, distillation may not effectively remove certain Volatile Organic Compounds (VOCs) which have a lower boiling point than water and can vaporize along with the steam.
Deionization (DI)
For high-purity applications, Deionization (DI) is often used, sometimes as a final polishing step after an RO system. DI removes remaining ionized solids using specialized synthetic resins in a process called ion exchange. Cation resins exchange positively charged ions (like sodium and calcium) for hydrogen ions (\(\text{H}^+\)). Anion resins exchange negatively charged ions (like chloride and sulfate) for hydroxyl ions (\(\text{OH}^-\)). These \(\text{H}^+\) and \(\text{OH}^-\) ions then combine to form pure \(\text{H}_2\text{O}\) molecules, which removes virtually all remaining dissolved mineral content and results in ultra-pure water.
Targeted Ion Exchange and Filtration Methods
Certain common water treatment methods are often mistakenly believed to reduce overall PPM, but they actually only address specific components or properties of the water. Water softening is a prime example, operating on an ion exchange principle. Softeners remove hardness-causing ions, primarily calcium and magnesium, and replace them with an equivalent charge of sodium or potassium ions.
Because one dissolved solid is simply replaced with another, the total mass of dissolved solids does not decrease. In fact, water softening may slightly increase the overall TDS reading depending on the valence of the exchanged ions. Therefore, a water softener should be used to reduce scale and protect appliances from hardness, not as a primary method for lowering the PPM measurement.
Standard sediment and carbon filtration systems are also not designed to remove the dissolved inorganic solids that contribute to the PPM reading. Sediment filters remove suspended particles that cause cloudiness, while activated carbon filters remove chlorine, organic chemicals, and compounds that affect taste and odor. While these filters are crucial pretreatment steps, they do not significantly alter the overall TDS concentration.
Another common misconception involves the effect of boiling water on TDS. While boiling is effective for killing bacteria, it does not remove dissolved solids. As the water turns into steam, the dissolved minerals and salts remain behind in the container, causing the concentration of the remaining water to increase. This means the PPM reading actually rises the longer the water boils.
Monitoring and System Maintenance
Maintaining low PPM levels requires regular monitoring and proactive system maintenance. A simple handheld TDS meter is the most practical tool for measuring the concentration of dissolved solids and establishing a baseline reading. This device measures the electrical conductivity of the water, which is directly proportional to the amount of ionized solids present, providing a PPM value. Regularly testing the water before and after the treatment system allows the user to calculate the system’s rejection rate and confirm its ongoing effectiveness.
For RO systems, maintaining pre-filters is required, as clogged filters reduce the water pressure needed to drive water through the membrane. The RO membrane needs replacement every two to five years to maintain the desired 95% to 98% rejection rate. Deionization cartridges require replacement or regeneration when their resins are exhausted, indicated by a rise in the output PPM. Distillers require periodic cleaning to remove accumulated hard scale and mineral deposits left behind in the boiling chamber. Consistent monitoring ensures that any unexpected spike in the reading is quickly identified, allowing for timely maintenance.