Can diet of 500 calories and 50-60 ounces water a day as well as moderate alcohol for more than a year be possible cause of, or lead to low potassium?

Bad idea. Inadequate intake of calories and protein, along with moderate alcohol intake ( don't know what you mean by that, but it is 1 drink/day for women, 2/day for men), can definitely set you up for fluid/ electrolyte/mineral in balance/ deficiency and lead to other problems.