I have a Omnitrolley system. The answer to your question.
Can depend on Water Pressure, Water Qailty, What type of RO unit you have. As Tell use abit more information then i can help.
Water Quailty TDS reading?
RO Unit 300 Gpd? 200 Gpd?
Water Pressure? 40 psi? 50 psi? 70 psi?
All these things can make a big differnents on the life span and the amount of water you can produce. As for the life span of the water once your produce it. It will last forevery as long as it does not become commtainated ie you mix tap water with it. If you just leave it once produced you can keep it the same TDS reading for ever.
Hope that helps but give us abit more information to help you.
Justin