Is there a water filter available that is so good that it would make our well water usable again?

This is a complicatedd problem.. and no you can't just install an RO membrane. You have solids in the water that will foul the membrane. And unless you're willing for fork over $$ for a whole house RO unit, then it's not going to solve the problem anyway. You'll spend a few hundred dollars and get a unit that produces 2 gallons per day for a few weeks. Then you'll need to replace the membrane for a few hundred $$.

My recommendation? call a professional in the water treatment business. Culligan e.g. They'll come out and analyze your water for you for free usually. Then they'll make recommendations. Which you can either do yourself or pay them to install.

My gut feeling.. you have sulfur compounds, iron, and solids in the water that needs to be removed. Probably hardness as well.

You'll probably need a prefilter, a carbon filter, a water softener that removes iron as well as minerals, acid injection to remove the sulfur smell, and a final filter. The prefilters could be wound, diatomaceous earth, or sand depending on the water quality.

You can google those and come up with some ideas on your own, but there are professionals that can design a system for you for free and ensure it is the right system for you.

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all that said, shallow point wells are pretty lousy. They contain a lot of contaminants from surface water. Especially ones that have a supply issue such as yours. You should seriously consider digging a new well.

The HyperClear water filtration is a good one if you take out small batches of a few gallons at a time. Ideally you should pre-filter through a coffee filter to prolong the life of the ceramic filter elements. It is non-electric and extremely low cost.

If you wish to run continuous flow rates the second link will give you some ideas, like what kind of treatment to use for the rotten egg smell.

The best filter that I can think of is reverse osmosis (RO) but expensive. RO removes suspended solid, dissolved solids as well as bacteria and smell.

The simplest is to have sand filter followed by activated carbon filter. Sand filter removes suspended solids and activated carbon filter removes smell and bacteria.