Yes, hard water is safe for dogs. Dogs are generally not adversely affected by this water since it contains minerals such as magnesium, calcium, and iron. However, some vets do not recommend giving water to your dog without first treating it. This is because of potential chemicals and additives, such as chlorine and fluoride, in the hard water. Yet, if they drink too much hard water, it can have a direct impact on your dog's overall health. Such water can cause abrasions and irritation to the lining of the gums and mouths. Therefore, check your water source to ensure there aren't any contaminants. These chemicals could be toxic if your dog consumes them. For instance, Lead may cause kidney issues.