In one of his Practical Engineering YouTube videos, Grady Hillhouse describes the phenomenon of water hammer. When the inertia of moving water is dissipated as the flow of water is interrupted suddenly, it can cause a severe shock. In some homes this manifests itself as banging pipes when water flow is stopped quickly by closing a faucet or the toilet valve shutting.
There are several mitigating strategies that can be taken to prevent water hammer, which can not only be annoying, but in large installations can cause water vessels to rupture or valves to fail.
Cushion of air
Whereas water cannot be compressed, air can. A bubble of air could be introduced into the pipe to cushion the water hammer.
Water hammer is dealt with in residential construction by introducing a column of air into piping or a dedicated hammer arrester in the flow of water before the valve. When the valve is closed, the inertia of the water is absorbed by the cushion of air, using Principle 29 – Pneumatics and Hydraulics.
I wonder if Principle 22 – Blessing in Disguise could find a role here. For example, could the inertia of water hammer be stored to enable some soft touch toilet flush?