We are buying a new house and our inspector found that if someone is taking a shower and someone else runs the sink, flushes the toilet, or if the dishwasher/washing machine is running, the shower practically turns off. I'm not sure what is causes this. Any idea?

Are you on well water or city water?

Chuck

Lack of volume at proper pressure is most-likely caused by undersized pipes. You will really never get rid of this problem until you repipe the house with properly sized pipes. You can "help" it a bit by increasing pressure - provided that option exists. While increasing pressure my give you more water (volume) to your shower head, it also comes with its disadvantages, like quite audible friction noise, more rapid deterioration of pipes as well as it puts strain on your plumbing fixtures.

Milo

I would have expected that your inspector should have carried this further by checking the psi and the cfm.

I agree with ballengerb1, It would be up to the inspector to report, and make sure this problem is addressed before the sale. Then you would know for sure what the cause is.

More information is needed without being able to check it. There may be many factors that can contribute to this situation.