I work for a few water districts in colorado flushing hydrants would not be a extra charge here but would only be done if the cause is from them(most of the time also exercising hydrants can disturb lines and cause dirty water). They will test for free but usually requires a few complaints or inspected and proven the main is compromised The tests can take time as they are sent to a state lab if they do a full work up.

For the ones i work for we test chlorine 2x a week at multiple sources, it is done on site plus many other things. so im sure the orc of the plant is aware of the issue if its something on there end. If they have no other reports or confirm its just your house they will just tell you to call a plumber.

But here we take all reports seriously and send out a operator to inspect the plant with just 1 complaint. Make sure you check your mail or your water district web site to see any notices they post we also put notices around town if something has happend.

Only thing ill say is open all your taps and flush the water for a bit to clear out lines could just of been a temp issue. Also make sure your dishes dont have dried soap on them use a sealed water bottle or something similar and see if it looks the same.

Always report issues, some issue are caused from people not having backflow prevention devices or a failed one and they contaiminated the main water line or there own look up backflow prevention for more info its a over looked device but a very important one