When should I install a pressure regulator?

Pressure regulator should be installed at a time when water pressure in your plumbing water system is significantly larger than the one at which water filtration system can be operated safely.  

For example, if User's Manual indicates that the filtration system that you about to install operates at maximum pressure of 3.5 bars (50.75 psi) and you plumbing systems operates at 4 bars (58 psi), then you must install a pressure regulator.