My toilet starting overflowing, but no one had used it for at least 30 minutes. The water overflowing was clear, so I don't think it's a sewer back up issue (this is not on a septic tank). What could be the cause?
Edit: I found out that the washing in an adjacent unit was running at the same time this happened. I'm not sure if it's related, but more details might help.
Best Answer
It's definitely a backup from a source higher up than the toilet. It could still be on the same floor of the house/building. i.e. The washing machine drainpipe is likely higher than the toilet.
The backup can be clear if the source is something like a shower, dishwasher, washing machine.
Since you are in an apartment, you should first contact your landlord before trying to clear the blockage yourself.