This looks like a pressure relief valve on the cold water line to my water heater. It is leaking outside. I've never seen a relief valve on a cold water line. Why
YA-15 Brass Relief Valve 1/1.5/2/3/4/5/6/7/8/9/10Bar Opening Pressure Safety Valve BSP1/2" for cold water pump protection pipe - AliExpress
Why the relief valve at the water heater is leaking, and what to do about it
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Everflow Ftgv-iso1-p-kit-lf 1" Pex Hot & Cold Tankless Water Heater Isolation Valve With Pressure Relief Valve Lead Free | Midwest Supply Us