Your supply is far better than most peoples inlet and flow will always fluctuate due to demand in your area in the morning and evening it will drop through the night and day it will be higher . i suggest you add aireators to the taps this will restrict to 5 litres a minute and fit flow restrictors on the showers this can cut them down to 8 litres a minute you can buy these through amazon online ,this should solve your problem and save water and money .
The problem is that the client is expecting all showers to be running we did offer an accumulator with boost set earlier on in the project but she said she did not have the funds for it now they are refusing to pay me my last payment saying the plumbing is faulty. Is there any minimum we need to give and to comply with bs6700 ?