"Well water" is a very broad term. What is your aquifer like, an alluvial basin (sands and gravels), fractured sandstone or shale, clay, artesuan, influenced by surface water either fresh or salt, former irrigated crop lands, industrial lands, underground fuel or chemical tanks nearby, septic systems or leach fields, deep well, shallow well, etc? There are many many variables in the well alone not to mention the pumping and pressure system.
I can tell you of some common issues with domestic wells such as elevated coliform bacteria, nitrates or ammonia from near by septic tanks, leach fields and sewage systems, elevated contaminant levels from things like agricultural run off or percolation through the soils, or leaking gasoline or fuel oil tanks. Many domestic wells have small captive air type pressure tanks with pressure switches set at around 35 psi which is sufficient for most uses but not enough to run a good RO and/or RO/DI system efficiently so a separate RO booster pump is required.
Most modern domestic wells require a siting study or survey so these things above are not an issue but older wells may not have been well planned out. Do you have a recent domestic well lab analysis for your well? The EPA suggests you have your water tested at least every 5 years for the common contaminants and asthetics and its not all that expensive. I almost always recommend RO/DI for a reef tank and if you have doubts about your water quality it is extremely easy to plumb a reef quality RO/DI as a drinking water system too and get dual use out of it. Most modern salt mixes are designed for RO/DI water so you have the perfect balance of ingredients when mixed and nothing is out of line. That way there is never a question in your mind if a problem is water related or not since you alone control its quality.
Other than pressure, a RO or RO/DI doesn't care if its well water, ocean water, raw sewage, surface water or whatever, it treats any and all of it just the same as long as you have a minimum of 40-50 psi and 60-80 or higher just increases its efficiency.