As RO- Water quality improves, the higher your differential pressure on the membrane is, a system with a permeatepump always makes better water. Let us say that your membrane reduces 98% of the TDS in your water if you got 60 PSI across your membrane. On 30 PSI differential it will only do about 95%. In the permeatepump system, you always see full line pressure across your element, which gives you always the maximum quality water out of you system.