This will allow you to smell the water without interference from the sink. Most odors of this nature come from a trap or garbage disposal. Be sure to keep these things clean and disinfected. The water I'm getting is yellow or brown. This may occur when a water main breaks or a fire hydrant is opened.
Lead enters the drinking water through lead based solder used to join copper pipes.
Lead solder was banned from use in 1986. Brass and chrome plated brass faucets is another known source of lead. Usually 15-30 seconds is sufficient. The City of Martinez has a corrosion control program to assist in the prevention of lead entering the drinking water.