If your water has a lot of alkalinity, boiling can be a semi-effective treatment prior to brewing. I wrote an article on Decarbonation by Boiling that is posted in the Ingredients section of the Forum. You need to boil for about 15 minutes for the reaction to be complete, but if there is much permanent hardness, you may not get the water much softer with the preboiling.
Your issue with iron could be troubling. That isn't removed by preboiling. You may be able to aerate the tap water by pouring it back and forth between buckets. The aeration can help convert the iron from a soluble form into an insoluble form and it can then be filtered out or it may settle out. That water can then be pretreated with the preboiling.
As you can probably gather, these steps could be a PITA. Getting your RO system back in operation may be more desirable.