You may have come across a water purification salesperson placing a simple electrolyte tester into tap water, and as it electrolyzes, yellowish solids begin to form in the tap water. As more and more of these solids form, the tap water turns into a reddish blur, that's when the salesperson declares the quality of your tap water to be problematic, and that you should purchase a water purifier. In reality, this is utilizing an electrolysis principle that most consumers do not understand to make a sales pitch. Tap water naturally contains some electrolytes （sodium, calcium, and magnesium etc.）, which conduct electricity.

The electrolyte testers that these salespersons use usually have metallic rods as anodes, and aluminum rods as cathodes, which, when immersed in water and electrolyzed, will cause metallicions to be released from the anode metal rod. This will immediately react with water and turn into a yellowish (reddish) hydrogenated metallic precipitation. If the anode is changed to an aluminum rod, then aluminum ions are released into the water. This reacts with water and produces a hydrogenated alluminum precipitation. Therefore, the murkiness created through electrolysis has nothing to do with the quality of the tap water, but from the anode rods used in the process.

Please DO NOT be fooled by these misleading electrolysis experiments.