At UCSB you may have up to four grades of water in your building: 1) industrial, 2) de-ionized, 3) polished, and 4) distilled. The only water in laboratories approved by the health department to drink comes from fountains.
Industrial water is drinking water provided by the city that runs through laboratory pipes which may not be adequately valved to safeguard it for human consumption.
De-ionized water (DIW) is on-tap in many buildings and has a spring-loaded handle by the sink. It is industrial water that passes through large yellow de-ionizing cartridges usually outside of a building or in a closet. These cartridges are managed commercially and may be changed manually or by an automated system when the electronic resistance goes below a threshold, often 4 M Ohms. This water is excellent for final rinses in many labs, but not recommended for sensitive aqueous reagents or sample contact.
Polished water is DIW that goes through a series of smaller cartridges to remove final traces of ions and organic contaminants. The resistivity is usually 10-16 M Ohms. These systems may be in each lab or continually circulating in loops of highly purified water in newer buildings. This water is excellent for most reagent needs and sample contact.
Distilled Water is DIW run through a still and often a polishing system to completely remove all ions. It is necessary for tissue culturing and trace element work, and should be used only as required.