Aerators are the fine mesh grid on your faucets that break up the stream of water by mixing in air. They are the device that allows you to have good water pressure but since the volume is 

reduced, you're saving water. They're mandatory to have on every faucet inside your home. But don't worry, faucets automatically come with aerators, so if you have never looked under your faucet and you don't have unreasonably high water pressure in a particular fixture, odds are you have an aerator.

There are only a couple reasons why you should consider cleaning or replacing your aerator: (1) you've noticed that the flow of your faucet has slowed down significantly. Often times when the water to your home or building has been shut off, the debris within your water lines will settle and build up at the aerator. Or, (2) you can see rust or corrosion around your aerator.

"Howe" to clean the aerator:

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