A chloramine filter is just a catalytic carbon filter that breaks the bonds of ammonia and chlorine, which make chloramine. The RO membrane will remove most of it afterwards. Adding DI resin will remove it all before it exits the filter. Once you have broken the bonds, chlorine can be vented in the atmosphere by letting it sit for a day, and ammonia is actually a food source for plants in low numbers (nitrogen). A 5 stage 75GPD RO filter will remove the vast majority of bad stuff from the water, DI resin will remove almost all of the rest, but for drinking and using on plants in soil, RO is what you want. You don't want to drink RO/DI as it will actually take out minerals from your body.
Yes, most RO and RO/DI filters have around a 95% rejection rate, meaning 95% of the water will be waste water while 5% will be clean water, which is why it takes so long to make.
www.thefilterguys.biz and
www.bulkreefsupply.com are the 2 places I order all my RO/DI filters from.