The real life house location used for the family home on screen doesn't actually fully connect to the garage, so the pool can be seen from the front yard. A facade was added to make it look like one full structure and to block the pool from the view in the front of the house.
The school that the kids attend is named Harold Holt. Holt was an Australian Prime Minister who was an avid swimmer and disappeared, and presumably died, while swimming in the ocean.
In 2018, director Rod Blackhurst and writer Bryce McGuire sold a feature length adaptation of their short film Night Swim (2014) about a woman terrorized in her pool by an evil spirit to James Wan's Atomic Monster. McGuire is set to direct.
Wyatt Russell's dad, Kurt Russell, was actually a very good minor league baseball player and would have made the MLB if it were not for an injury.
All the mythology came from writer/director Bryce McGuire's own mind, although he was generally inspired by various established mythologies. The word Temagami may sound Japanese, but it actually comes from an Ojibwa word from the Great Lakes region of North America. It does mean roughly deep water as Jodi Long's character says in the movie, but other than that, there's no direct legend about healing waters in the Ojibwa culture; the most prominent connection to water is a being called Mishipeshu, an underwater panther-like creature. McGuire mainly took inspiration from legends involving wishing wells or healing springs; most people are familiar with the idea that if you throw a coin into a well or even a fountain - in other words, make a sacrifice - you might be granted a wish. In an interview with NBC Insider, McGuire says he researched various cultures with spiritual connections to water, including Celtic mythology and the Sacred Cenote from Chichen Itza. He also took inspiration from the Bible, specifically the supposed healing waters of the River Jordan. He says he wanted to explore the give-and-take relationship these cultures have with water, hence the idea that the pool in Night Swim demands something in return for its blessing.