We live in a condo with a shared wall. When the neighbor turn on their water it's loud. What can be done about this
Small diameter pipes can be noisy, but fitting larger pipes while the « solution » now can be difficult and expensive.
Usually happens when a small pipe feed an area which then has a change of use and the water demand increases which increases the speed in the small pipe.
Usually on domestic pipes the speed should be kept below 2 m/s while hydraulic systems can be up to 7m/s.