I've used a RO System for the last year without di vessels as it comes out pretty pure, only a couple off 000. But it uses a lot of water as it's only the 300GDP (lies) system. Now, I know some people here only use DI vessels as their water from tap isn't full of too much rubbish, and I was debating trying it, the tap water is around 130ppm. Today I ran it straight through the DI Vessel as was rushing and it got me thinking. Granted the resin will need replacing more, but at the same time, I'll be saving money on the water bills, as I'm using FAR LESS water to purify, no waste water. Is it worth it? As I don't know how long resin will last on its own. Help needed. Thanks.