Dupes, unlike ordinary water, cannot consume polluted water. It can be used for the production of fertilizer or irrigation of certain plants. Pincha Pepper and Thimble Reed consume polluted water to grow (35 kg and 160 kg per cycle respectively). Like any other liquid when dupe steps on spilled polluted water or dives in – he receives a negative status that can raise the overall stress level. Thus, simple liquid locks can be very stressful for your colony by design.
Dupes themselves can create polluted water contaminated with food poisoning germs when there is a problem with the toilet or when stress vomiting. Besides showers and lavatories creating polluted water every use. Note that lavatory creates more water than consume (-5 kg of clean water and +11.7 kg of polluted water per use).
It has advantages over clean water – 20 degrees lower freezing point and 20 degrees higher evaporation temperature with the same specific heat capacity. This means a great liquid cooling agent. After evaporation, it becomes steam (99% of mass) and dirt. Although cleaning polluted water this way is disastrous ineffective due to a huge amount of power consumption on boiling. Water Sieve is a more suitable choice and it generates more polluted dirt, which is a really valuable resource for farming.
Over time and if surrounding pressure less than 1800 g polluted water "off-gassing" into polluter oxygen with mass conversion 1:1. Still, the process is quite slow (1000 kg tile emit ~2.4 kg of polluted oxygen per cycle) unless polluted water filled in a bottle. Bottled polluted water off-gassing at an unbelievable rate and can be used as a secondary oxygen source (better with oxygen deodorizer).