Why is the water in swimming pools usually blue?

The water in baths is usually blue because the disinfectant copper sulfate is added, and its aqueous solution is blue and can kill viruses. In addition to copper sulfate, there are also disinfectants such as bleaching powder and alcohol, but alcohol is not suitable for bath disinfection. Safety procedures must be followed when using disinfectants to protect human and environmental health.

In people’s minds, green and transparent water is clean water. Why is the water in the bathhouse usually blue? This is when people add the disinfectant copper sulfate (CuSO4) to the water. Copper sulfate is a heavy metal salt, and its aqueous solution is blue (the color of hydrated copper ions). The divalent copper ions can denature the proteins that make up the virus, thereby killing the virus. Copper sulfate is a commonly used pool disinfectant and is used to disinfect aquatic plants and fish gear. CuSO4 is used in aquaculture, especially as a common drug to prevent and treat fish diseases. It can also kill parasites, especially protozoa and some lower algae, and is very effective in treating fish protozoan parasitic diseases.

Of course, the water in some bathtubs is not blue. It may be that other disinfectants such as bleaching powder (the active ingredient is Ca(ClO)2) are put into the water. Calcium hypochlorite is a colorless aqueous solution dissolved in water. Hypochlorite (ClO-) is used to kill viruses. The positive monovalent chlorine element in hypochlorite has strong oxidizing properties and can destroy the structure of viral proteins and nucleic acids. Adding 0.3 to 1.5 grams of bleaching powder per liter of water can be used to disinfect and deodorize drinking water. Bleaching powder is mainly used for disinfection of pens, feeding troughs, utensils, vehicles, etc. It generally uses a suspension with a concentration of 5% to 20% for spray disinfection. However, it should be noted that bleaching powder cannot be used to disinfect colored cotton fabrics and metal utensils, and cannot be stored together with flammable and explosive materials.

Alcohol is also a commonly used disinfectant. Why not use alcohol to disinfect the bathtub? In fact, alcohol disinfectant with a concentration of 75% can be used to disinfect human skin, especially when wounds appear on the skin surface, to prevent further aggravation of wound infection symptoms. However, alcohol solutions with lower concentrations have poor disinfection ability, so alcohol solutions are usually not used for bath disinfection. Alcohol disinfectants are generally used for surface disinfection in public places, such as shopping malls, supermarkets, parks, etc., as well as household items, such as socks, shoes, sofas, etc.

In short, the blue color of the water in the bath is due to the disinfectant copper sulfate, which reduces the risk of virus transmission through the bath. If there is no disinfectant in the bath, there is a risk of virus attack if everyone shares the same bath. It is disinfectants that protect people’s health and safety.