Urine is generally fairly sterile while it is inside the human body, except when the individual is suffering from a kidney, bladder, or urinary tract infection. However, while passing through the urethra on its way out of the body, urine often becomes contaminated with bacteria that are present on the outside of the body or even within the urethra itself.
Ordinarily, this would not be a problem, as bacteria require a warm, moist environment in order to thrive and multiply. As the urine cools and dries out due to evaporation of the water, any bacteria present will die fairly quickly.
Unfortunately, flush-type urinals create exactly the right kind of environment for bacterial growth. The almost-constantly-wet ceramic surface provides moisture, and damp surfaces also tend to retain heat better, so these two factors in combination actually encourage bacterial growth.
Other reasons why flush urinals propagate and spread bacteria include:
- There are often substances present in water that serve as a food source and help bacteria grow.
- The flushing process may allow small amounts of mixed water and urine to splash onto the bathroom floor and surrounding fixtures and thus poses a risk of the bacteria being moved from place to place by human activity.
- The flush button or handle can easily be contaminated by bacteria as a result of splashing during flushing, and this is then moved from place to place by users – possibly ending up in and contaminating handwashing basins and faucets.
Because it dries out very soon after use, a waterless urinal will harbor far less bacteria than a flush-type urinal, and any bacteria that do survive contact with the dry ceramic surface will end up below inside the cartridge, where they can’t do any harm.