If you open the tap in the morning and see blue water flowing, you might be tempted to look out the window to check if aliens have arrived, especially in 2021. However, in reality, blue water periodically appears in cities across Ukraine. The last instance was in Mykolaiv in October 2020. Prior to that, it appeared in Chornomorsk, Odesa, Kyiv, and Berezhany in the Ternopil region—like a ghostly water phenomenon. In fact, blue water from the tap usually indicates chemical contamination, and the types of contamination can vary.

Blue copper water

Many people remember the beautiful blue solution of copper sulfate from their school chemistry course, which was once used to treat trees and living spaces for mold. This and its relatives—copper salt solutions—are often the basis of the blue water that appears from the tap.

A light blue tint, which intensifies when mixed with soap, may occur when using copper plumbing and pipes. This problem is often accompanied by a blue residue in the sink or toilet.

So, why isn’t copper present in the water everywhere copper pipes are installed? It depends on the composition of the source water—if the water is acidic with a high content of carbonic acid, chlorides, sulfates, and is heavily oxygenated, corrosion will be quite active, and the corrosion products will settle on the plumbing, coloring the water. Corrosion can also be exacerbated by the presence of iron, aluminum, and other metals in the water.

The maximum allowable copper content in drinking water is 1 mg/L, in which case the water will not have color, but it may have a metallic taste. If the copper content exceeds the permissible level, the water will take on color and form deposits on plumbing fixtures and laundry during washing. Sometimes, when using copper pipes, the copper content in the water can exceed 5 mg/L. Since copper is a heavy metal, it can cause certain health problems, so it is not recommended for drinking. The issue of copper water can be resolved by using domestic reverse osmosis, replacing all the pipes, or employing a skilled plumber who will install proper connections at the points where copper and steel pipes meet, where galvanic corrosion is most pronounced.

Blue water — The phantom

If copper pipes are understandable and the phenomenon is usually stable, the "Martian water" that periodically appears in the taps of residents in various Ukrainian cities is more complicated. One morning it’s there, and by evening it’s gone. The answers to questions about its origin are always different, but from what we've found online, it seems to be:

• The installation of a toilet tank without a backflow valve, when slowly dissolving agents added to the tank not only color the water when flushed, but also return to the water supply system. Often, the blue liquid has an unpleasant smell and foams.
• Flushing of water supply systems after planned or emergency repairs with copper sulfate and other reagents. In these cases, the water quickly runs off and turns the familiar color.

The most interesting thing is that utility services cannot provide an answer about the origin of the blue or blue-colored water, and we have not found any analysis results of the blue water online. It’s worth remembering — if what’s coming out of the tap looks and smells different from water, do not drink it, wash dishes, or bathe children until the cause is identified.