Hey DV;
I am the veteran of many sinus infections. I am also a Water Treatment Plant Operator, so I know a little bit about Nagleria Fowleri, aka, the brain eating amoeba. First, I must state that daily saline irrigation of my sinuses has made sinus infections a thing of the past for me. Even if one gets started, saline irrigation destroys it in a day or two. Like you, I was quite concerned about Nagleria . The big fear is that we don't look for Nagleria in drinking water. You can ingest Nagleria all day long through drinking, and nothing will happen. It is only a hazard if it enters the nasal passages. Nagleria is quire rare in drinking water systems, primarily because it is extremely susceptible to chlorine. The only drinking water system that I am aware of where nagleria was detected was in New Orleans. That was in a main that was little used and the chlorine had dissipated. That makes the water a playground for a number of pathogens. Most cases of Nagleria (all that I am aware of) were spread in a swimming environment, ponds and lakes. Again, the chlorine in a swimming pool will take care of business.
Nagleria is scary as hell, of course. I take no cahnces even though I know that it has zero chance of surviving the chlorine in the city lines. Just to be safe, I add a couple of drops of Hydrolized silver water to the nasal irrigation. That provides disinfection and anti-biotic effect as well. I am familiar enough with the disease and it's environment to deal with it comfortably. In the end you have to live with the sinus issues, so you have to decide on the degree of risk and effort that you are willing to assume, after all, it isn't safe to get out of bed in the morning.
Jim