How hard does water have to be forced up the nose for the brain eating amoeba n fowleri to infect you?

It doesn't. There is no pressure gradient required for Naegleria fowleri in endemic waters to infect; it migrates when in the trophozoite form after attaching to olfactory axons and into the brain through the cribiform plate.
Agree with Dr. Liang. There have been no reports that excessive force is needed for N fowleri to be transmitted.

Related Questions

I am from Louisiana & my parish informed us the water tested positive for Naegleria fowleri "Brain eating amoeba. " How easy is it to become infected?

Not easy. You would need to be bathing in it and water would need to get into your nose. See this site for more information and do not worry. http://www.cdc.gov/parasites/naegleria/illness.html. Read more...
Very, very rare. In June 2017 drinking water testing by the Louisiana Dept of Health confirmed N. fowleri, in Ouachita Parish’s North Monroe Water System & Terrebonne Parish’s Schriever Water System. REF: https://www.cdc.gov/parasites/naegleria/public-water-systems-louisiana.html When it has been found previously in Louisiana (rarely) improvements were made to water systems and there were extra flushings. Read more...