I heard that the water pressure in the mainline is less than normal when it rains. Is this true? I would like to confirm if there's a real reason behind it. Even if your washing machine operates normally, there will be water leaking at its joints and connections due to ground settlement or aging of pipe materials as years go by. Since such water leaks are invisible during normal operation, you could think that the pressure of the water supply has decreased. In addition, even if there is no leaking from home piping, it could be difficult to understand the real reason for this summer phenomenon. First, it is important to measure the water pressure at a fixed point so that a drop in pressure can be confirmed reliably. Let's see how the water pressure changes with rainfall or during normal operation. If the area where you live has already completed maintenance work on supply piping, there should be no problem as long as there are no leaks from home plumbing connections such as washer and washing machine dispersion detergent dispenser joints, faucet joints, and bathroom pipe joint. After all, it is normal for the water pressure to drop when the rain falls. When there is no rain, the water pressure will rise again as a result of excess supply from the company. On the other hand, in some cases, it may not go back to normal even after 3 or 4 days even after rainfall stops. This can be explained by connecting with underground water (artificial groundwater), which changes according to precipitation and evaporation levels in surrounding areas. In this way, there are many factors that affect the water pressure in your house so I think you should check if your home has any problems with joints or connections before thinking about global reasons.