By the way, up to half a liter of water can accumulate on cold water risers per day. Due to excessive humidity, mold often appears on the pipes.
How to properly insulate a pipe
To solve this problem, you simply need to insulate the pipe with a special insulation called “foamed polyethylene”. It can be found in hardware stores. Insulation is sold in different diameters and thicknesses. For a cold water riser, you can choose insulation with a diameter of 42 millimeters, and for smaller diameter pipes - 22 millimeters.
First, you need to thoroughly wipe the pipe dry with toilet paper to remove moisture and dust. Then, using a tape measure or flexible meter, measure the required length of the pipe section, mark it and cut off a piece of insulation with scissors.

Insulation installation
Cut the insulation lengthwise with a utility knife to make it easier to put it on the pipe. After that, wipe the pipe again with paper so that the surface remains completely dry. Put the insulation tightly on the pipe and secure it with tape. First, secure one part with tape, and then gradually wrap the entire surface.
If there are complex sections of pipes, for example, adapters or taps, we take the necessary measurements. We cut out the necessary shapes from the insulation and carefully fix them with tape. If the insulation does not fit in diameter, you can use additional pieces and construct a part of the required size.
In this way, we insulate all sections of the cold water pipes, creating complete insulation. The work is done, and now the cold pipes remain dry, and the hot ones are not covered with condensate. Problem solved!