Understanding Total Dissolved Solids (TDS)
Total Dissolved Solids (TDS) refers to the concentration of dissolved particles in water. These particles can include minerals, salts, metals, and organic matter. In the context of cleaning, TDS is the single most important factor determining whether water will dry "clear" or leave behind visible spots and streaks.
When ordinary tap water evaporates from a surface, it only leaves behind H2O molecules. Everything else that was dissolved in the water—the TDS—stays behind on the surface. These are the "water spots" you see on windows, car paint, and glass.
What Makes Up TDS?
Typical tap water contains a variety of dissolved substances, including:
- Minerals: Calcium, magnesium, and potassium.
- Salts: Sodium, chloride, and sulfates.
- Metals: Iron, copper, and lead (in trace amounts).
- Carbonates: Bicarbonate and carbonate ions.
The "hardness" of your water is largely determined by the amount of calcium and magnesium it contains. The higher these levels, the more difficult it is to achieve a spot-free finish without deionization.
How TDS Affects Your Cleaning Results
The relationship between TDS and cleaning quality is direct: the higher the TDS, the more residue is left behind. Professionals categorize water purity based on its TDS reading, measured in parts per million (ppm):
- 0 ppm (Pure Water): The gold standard. This water is "hungry" to pull dirt off surfaces and evaporates 100% cleanly, leaving zero spots.
- 1-10 ppm: Very high purity. Usually sufficient for most window cleaning and detailing tasks without visible spotting.
- 50-100 ppm: Typical filtered water. May leave faint spots, especially on dark surfaces or in direct sunlight.
- 200+ ppm: Hard tap water. Will leave significant mineral deposits and streaks unless manually dried with a towel.
The "Hungry Water" Effect
One of the hidden benefits of 0 TDS water is its increased solvency. Because deionized water has been stripped of its minerals, it is chemically "unbalanced" and seeks to return to a neutral state by dissolving minerals and dirt it comes into contact with. This makes it a more effective cleaning agent than tap water, often eliminating the need for soap or detergents.
How to Measure TDS
Measuring TDS is simple and inexpensive. Professionals use a handheld digital TDS meter, which measures the electrical conductivity of the water. Since dissolved solids are ionic (electrically charged), the meter can accurately estimate the concentration of solids based on how well the water conducts electricity.
To get an accurate reading:
- Use a clean glass or container.
- Rinse the container with a small amount of the water you are testing.
- Fill the container and dip the meter's probes into the water.
- Wait for the reading to stabilize.
Achieve 0 TDS Every Time
Don't leave your reputation to chance. Use ASTM-certified deionized water to ensure your cleaning results are always spot-free and professional.
Learn More in Our Lab Water Guide →