New answers tagged thriller
It was not The Hitchhiker, but Pee-Wee's Big Adventure, and the woman truck-driver was Large Marge. Here's the clip.
Your recollection matches a section of the IMDb synopsis for House (1986). There are too many details to quote it all, but it mentions the father seeing his son behind a mirror in a painting, breaking the real mirror, entering "another dimension" where there is water, rescuing his son from monsters and emerging through a swimming pool.
Top 50 recent answers are included