It’s possible that from time to time your water may be safe to drink, but is discolored for some reason. The primary cause of water discoloration is due to naturally occurring minerals (primarily iron and manganese) flowing with the water. These minerals, which are heavier than water, settle in water pipelines when water usage is low - especially during winter months. When the water flow and pressure through the water pipes increases again (due to irrigation, construction, etc.) the minerals are stirred up and flow out of your faucets when you turn on the tap.
The Department of Public Services "flushes" the water system twice a year; this also allows the City to remove any sediment from the water lines which helps improve quality and clarity. As a result, water main flushing can cause temporary changes in water pressure or discoloration.
Find helpful information on Water Discoloration from American Waterworks Association.