If you are not impacted by a water main break in your area, it is very likely that you are experiencing lower water pressure due to a pressure relief valve (PRV) going out in your home. A pressure relief valve that needs replacement will cause intermittent low pressure, continuous low pressure, or possibly a complete water outage. In addition, you may hear loud noises in the line or a rattling of the water lines. A pressure relief valve is usually located where the main water line enters the home. These are best replaced by a licensed plumber.