They are connected directly to the water line. NSF Certified - NSF is a nonprofit, independent organization with more than 50 years experience in testing and certifying products to ensure they meet strict public health standards. For a system to become NSF Certified, it must meet not one but five basic requirements. Contaminant reduction claims are true. System does not add anything harmful to the water.
System is structurally sound.
Advertising, literature and labeling are not misleading. The materials and manufacturing process used don't change, meaning consistent product quality over time. All distillers go through the process of distillation. One brand distiller will not significantly make purer water than another brand. Pyrex Glass is the cleanest material to heat water without adding contaminates back into the water.