What grade of copper pipe ( type K, L, or M) should be used for an underground supply line from the meter to the house in San Diego to meet code requirements?

San Diego requires copper? Living in old times! Lines today are typically PVC, PE or PEX. Copper corrodes in soil, particularly if acidic.

https://www.sandiego.gov/water/cip/guidelines.

City of San Diego code "approved
services-Water Services ............... PVC, Copper Tube"

If they demand Copper, use K, the thickest wall pipe.

Yup... Type K copper is the only copper tubing allowed underground anywhere that I know of.

In So.California, you use type "L" copper under ground. Type "L" copper is rarely used, and certainly not required by Code
However, type "L" is heavier schedule copper pipe. It certainly can be used if you are OK with spending twice as much as for schedule "L".

However, as mentioned above, copper already fell out of favor and is on its way out. There is just way too many problems with copper. I suggest you use PEX pipe underground which is now commonly used by plumbing contractors all over So.California

Good luck with your project !

Milo

Correction to my previous post. Should say: ".... type "K" copper is rarely used ..... " and... " type "K" is heavier schedule copper pipe.... "

My apology for the confusion

PS: If I recollect correctly, only City of Industry in So.California requires type "K" copper every time copper is used, regardless of location, or type of use


Milo