The most likely explanation is that the membrane is not inserted fully into the housing. This will allow water to bypass the membrane and drain out through the good water line. Unscrew the cap to the membrane housing and push firmly on the membrane until it will not go in any further. It is also possible that the product and waste water lines have been crisscrossed. Simply switching the lines will correct this. The good water line will be the line centered on the rounded end of the of the membrane housing. The wastewater line will be on the same end but comes out through a fitting offset the center.