Taking a picture of dirty water is one of the optional side quests you can complete in Phasmophobia. You won't always receive this task, but it's worth knowing how to complete it if you do.
To spawn dirty water you will need to find a sink. Most Phasmophobia maps contain at least one well, so you shouldn't have a problem locating one. Running dirty tap water, instead of clean water, is up to the ghost, not you. If you interact with the sink by turning on the faucet, you will only get clean water. So, how do you run dirty tap water during phasmophobia?
The first thing you need to do is make sure that a member of your party takes the camera with them from the investigation truck. You will need this to take a picture of the dirty water as evidence. Once someone has it, enter the house or building and find a sink. You can find one in the kitchen, bathroom or toilet.
Make sure your entire group is in the same area. The ghost is more likely to get angry if the four of you are in the same room. Start asking him questions and, if you find out the ghost's name, start repeating his name again to frustrate him even more.
Once you think you've bored him enough, have the ghost turn on the water. If you are successful, dirty water should start flowing through the faucet. Take a photo of it as proof.
Be aware that the ghost might turn on a faucet in another room, so listen to the running water elsewhere in the house. It is also worth nothing that whatever room the dirty water begins to flow into means the ghost is in that area of the house. Prepare for a possible encounter with him if you see or hear dirty water.
Some players claim that they have turned on a faucet, seen clear water to begin with, then noticed that it turns to dirty water when a ghost enters the room they are in. This method is very hit and miss, however, so it's best to follow the above formula to get dirty water every time.