Economic Low Energy RO Membranes For uncompromised water quality when cost is your main consideration, the specifically designed, fibreglass wrapped CS-4040 deliver new standards in quality and performance for economic RO membranes, making them a perfect choice for the competitively priced market. With rejection rates of 98.5% the budget range stands shoulder to shoulder with industry established pure water production membranes whilst competing in price with entry level imported inferior alternatives.