Earlier quoted context omitted.
Your local university extension should be able to provide this service at a reasonable cost ($100-$500, depending on what is being tested for). There are commercial water testing firms, but I do not have experience with any that I could recommend. https://www.nifa.usda.gov/about-nifa/how-we-work/extension https://www.isws.illinois.edu/health-environmental-applicati...
Instead of testing for every one-off thing that comes up, maybe just go with a small reverse osmosis system for a similar price range.
A quality iron/hydrogen sulfide water filter sets you back about $2k, and will last ~10 years or ~500k gallons. If you do not have this in your water, you can safely skip. High iron can lead to iron reducing bacteria scumming up fixtures and, more importantly, rapidly dissolving a hot water heater tank. If you smell sulfur in your hot water when you shower on a well, that bacteria is eating up your tank's anode rod quicker than normally would (I also suggest a powered anode rod, good for 20+ years to keep a tank tip top vs having to replace consumable anode rods, but that is another topic). A three cartridge system will cost you a few hundred dollars for setup, replacing the cartridges roughly every year after ~100k gallons of water has passed through them (~$100-200/year, depending on cartridge filter selection). You can mix and match cartridges for your specific water contaminant filtering needs (sediment, iron, heavy metals, VOCs, pesticides, etc). I would agree with optimizing for use case, but RO systems can be costly and high maintenance depending on the demand put on them. They are ideal for low demand, low flow applications like a kitchen faucet or refrigerator water supply for water and ice. Design accordingly.