A color dye usually used in concentrated gels for soft drinks was added to the water to turn it to a dark color.
The heartbeat heard during Dahlia's migraines are from an ultrasound scan of Daniel Rezende's wife who got pregnant at the beginning of the shooting.
When Dahlia moves her wet clothes from one washing machine to another, you can see the number, "666", pop up for a moment on the second washing machine. That number is known as the symbol of the Anti-Christ.