EC meters are Electrical Conductivity meters, and they are used to test the PPM (parts per million) of your water. This is the rating that is used to decide how concentrated your water is, and how much nutrients and fertilisers are in the water. This is important in any growing room, even if you use hydroponics or a soil medium. This is because when plants are young they cannot handle a large amount of nutrients at once, so taking a reading every day is important for plant health. It also helps you to regulate the amount of nutrients you add to the water tank.