How to effectively utilize water discarded by RO machine?

(Query received over email from Krishna Shastry)

Could you kindly help me with some information on how to effectively utilize water discarded by RO machine? Following is my current understanding and thoughts:

Collection within individual apartments vs. in common place
Collection of such water within individual apartments needs discipline and some infrastructure changes. Looking at general trend this won't happen in most homes. In apartment complexes, I think the best way would be to introduce separate/small pipe system and collect this water in a common place. Maybe such small pipe system can be installed with only a small contribution from each apartment.

Which common place? Treatment tank or rain water harvesting tank?
This water is really not dirty, its just that its hardness/mineral content is different. Is it okay to feed this to rain water harvesting system or should we just release this to waste water treatment system? What do you think? And if destination is anyway the treatment system, then just leaving this water to go down the drain is not a big deal, isn't it?

Watering plants/garden: I hear from some people that it spoils the soil in the long run.

Cleaning floors: Some people scare us by saying that using such water to clean floors might result in 'deposits' on floors/edges and might be destructive in the long run.

Toilet flush: Many people think this might be okay. But again there is a question about 'deposits'.

Regarding the utilization, my question is - isn't the quality of output water actually dependent on water input? In general what do statistics/researches say?

I hope to get some guidance from you on this.

Krishna Shastry