If you are concerned about your water, you can collect a sample in a clean glass container and send it in for analysis (to who varies by local and you would likely pay. Your State may have water quality info). Neurologist would be the doctor to see. MGUS is considered asymptomatic, however, neuropathy is one of the potential early symptoms. I have polyneuropathy (8 years, 70 yo) diagnosed about the same time as MGUS; in my case a lack of sensation, less feeling in my lower legs and decreased pain that hasn't worsened over time. If changed sensation is affecting your balance it would be good to get PT for that. MGUS is a waiting game; progression to SMM or MM is only 1% a year so for most people it stays as MGUS. It is caused by a mutation(s) in bone marrow plasma cells and generally no known cause. Recommended are a healthy diet (low sugar and such), regular exercise, managing stress/sleep. Some people take curcumin supplements (an ingredient in turmeric). Here is some MGUS info: https://pmc.ncbi.nlm.nih.gov/articles/PMC7604635/#:~:text=Monoclonal%20gammopathy%20of%20undetermined%20significance%20(MGUS)%20is%20a%20common%20benign,(MM)%20and%20related%20disorders.&text=MGUS%20is%20considered%20asymptomatic%20but,with%20peripheral%20neuropathy%20(PN).