Public officials should be banned from trading individual stocks for numerous reasons. An officials duty is to serve and protect the public interest, and the people. Most officials have a set salary, and usually it is good enough to pay to have a nice life. If public officials are allowed to trade stocks, they will likely prioritize that, instead of their true purpose to serve the people, as a main focus because it would make them more money.

Yes, but as an elected official, there are numerous other mechanisms and ways to help a local water company rather than just investing in them. Many people who aren't politicians can invest in them if they truly care. The fact is that most people do not want to invest for moral reasons, and are seeking to make money. And it has happened numerous times where politicians will do anything they can to stay in power and especially make money. What stops a politician from buying stocks from a country that is known to have inhumane practices? We cannot dismiss the obvious problem because of one exception.

But we cannot rely on politicians to completely follow the rules. Corruption is a problem in numerous countries and cities in America. Politicians have and still they find shady ways to make money so we can't rely that they would simply follow all the rules. Also, you say that a politician shouldn't have to give up their own money to serve the public but I disagree. While it is a fact that politicians do get significant donations from companies in their campaigns, many of them spend their own money on that. And if they were to invest they would be spending their own money. So why are they allowed to spend their own money for personal gain but not for helping the people which is the purpose of their job?