Nightmare at Noon (1988) on Netflix

Plot summary

In the isolated Utah town of Canyonland, a scientist called the Albino injects a substance into the water supply with the help of a shadowy agency. Residents who drink the water become homicidal maniacs, killing each other and anyone who passes through. A group of visitors in a recreational vehicle arrives and sees the violence. Remembering something unusual at the river on their drive in, they suspect the water is the cause. They try to warn city officials and find a way to reach the outside world, but the Albino has already cut off all routes out of town and all communication.