Variable water pressure

I live in a fifth-floor flat. Recently the council installed a new pump to raise the water pressure in the block of flats. Now, the pressure of the water coming out of the taps fluctuates from one moment to the next. More importantly, my power shower no longer works properly. Sometimes it works fine, but at other times the water flow cuts off suddenly and the pump races.

Is it possible that there's a problem with the main pump, or should I just concentrate on dealing with the problem in my own flat? (In other words, is variable water pressure sometimes just a fact of life?) I have thought of fitting a regulator to the supply pipe going into the shower. Is this likely to solve the problem, or will I have to replace the shower with one that doesn't have a pump? Thanks very much for any advice.

There is some information missing here.

Does the council pump fill a header tank from which you draw water, and then pump it yourself?

Or is the council attempting to provide a mains pressure water supply to your flat without a tank storage?

I suspect the former, and it sounds like you are pumping their/your tank dry.

Yes, there is a header tank on the roof of the building. (It's a large block - nine stories, around sixty flats in total.)

Do you have a smaller tank in your property fed from their large one?

If so, this isn't filling as quick as you are emptying it, so you will need to increase the size of your tank or take shorter showers.

If you are running off a central tank, you may be draining it, or when the council upgraded it, they may have fitted flow restrictors to each flat which stop you from influencing the amount of water available to other users. You could measure this using the bath taps, if the flow rate has diminished then there is a sure sign that some tweaking has been carried out.

There's no separate tank - I'm running off the main tank. It's difficult to tell from the flow through the bath taps - it looks about the same to me - but the flow restrictor sounds likely. I had the same shower before - when the water pressure was lower - and I never had any problem with it.