system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does the fire department drain the fire hydrants and why does it turn the water in my house yellow?
gpt
There are a few possible reason to open the hydrants (just be aware that they won't drain as they are connected to the city's water).

1) They are testing the hydrants for pressure. This allows the firefighters to know they will have enough pressure on the hoseline if they ever have to use it in a fire.

2) They were doing some form of maintainence or repair on the hydrant.

3) They were opening it up to clear any debris/ garbage that someone may have put into the hydrant.

The reason why your water might change color is that both your house and the hydrants run off the same water source. Seeing as the flow of the hydrant is quite high, it will dislodge some fine particles in the system that will mix with the water to give you that color. It is perfectly safe.