Low Tide shows a few days in the life of a boy in Texas living with his reckless, fun-loving, poor, hardworking mom. He's her only child and he's the only "steady", stable male in her life. The men she sees drift in and out; she sleeps most nights alone.
The boy's life is hard and sad, and his torment steadily grows until one night he escorts his mom to a bar at night and she leaves without him. He walks home in the dark alone.
At home, he rounds up the dirty laundry, puts it into the machine, and then, seemingly impromptu, forces himself to drink down laundry detergent several times so he gets very sick.
The end of the film shows his mom fetching him from a hospital and then driving him to what we take to be a place he particularly likes and rarely sees: a Texas Gulf beach, where they both reconnect and share an all too rare moment of qualified happiness.