Dental unit water quality standards require that treatment water contain no more than how many colony forming units (CFU) per milliliter of heterotrophic water bacteria?

The CDC and EPA standard for dental unit water quality requires that water used for routine dental treatment contain no more than 500 CFU/mL of heterotrophic water bacteria. This standard aligns with the EPA's drinking water quality standard. Untreated dental units cannot reliably achieve this standard because biofilm accumulates in the narrow-bore tubing of dental unit waterlines. Dental practices must use water treatment systems, monitor water quality regularly, and use sterile water or saline for surgical procedures. The original question was poorly worded; this reformulation clarifies the actual regulatory standard.