Testing Purity of Water Used for Reach and Wash Window Cleaning
September 17th, 2015
After the reverse osmosis and de-ionisation stages of filtration are completed, purity is tested using a TDS (Total Dissolved Solids) meter to ensure the level of total dissolved solids (e.g. minerals such as calcium, magnesium, potassium) is low enough to be used for window cleaning.
To get an exact measurement of the TDS, the sample would need to be evaporated, then the residue weighed.
This residue could be seen if glass is washed using tap water, residue would appear as white spots or streaks when dry.
However this is impractical, so a TDS meter is used to give an approximate reading.
A TDS meter is actually an EC (Electrical Conductivity) meter which measures the conductivity in micro-Siemens across a specific distance.
The more inorganic chemicals (impurities) present in the sample, the higher the conductivity of the sample, due to the increase in ions. TDS meters available give accuracies between 1% and 2%.
We test the product water to ensure the TDS meter reading is below 10 ppm (parts per million), but the closer to zero ppm the better. Generally for Reach and Wash window cleaning, water should be used that has a TDS reading between 0 and 3 ppm, to ensure a consistent result.