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 entity inhabiting the pool is referred to as Temagami. It's an indigenous word of Algonquian origin, meaning "deep water". In Ontario, Canada, it's an umbrella term used for one of the local municipalities, its corresponding lake and river, and the First Nations tribe living in the area. This adds further verisimilitude to the film's internal mythology, according to which the water in the pool originates from a natural spring that has existed for centuries.
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.
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.
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.