is needed, it will allow you to check the the water to see when the filters and DI
need changing. I check the water out of the tap, then after the membrane and then after the DI
. As the TDS
raises I like to change out the micron and carbon. When you see TDS
after the Di
you should think about changing it. Remember TDS
meter will not pick up phosphates or silicates so if you have them in your tap you will need to check for them once in a while in your ro
PSI is a nice to have.. is it needed no. If you have low water pressure it will effect the output of the unit so if you know your pressure is low then I would say you don;t need a PSI gauge to tell you that.