Is it well water?

Tap water from the local supply.

Maybe I will ask the question on the local Facebook neighborhood group and see if others have the problem.

"Tarnish is a chemical reaction between silver and environmental sulfur, which is found in water, wool, felt, and even the air we breathe."

Found on southernliving.com.

Moisture can accelerate the oxidation process, and silver doesn't need a lot of exposure to oxidize. If your water has a higher-than-normal sulfur content, it will oxidize more rapidly. There are plenty of explanations online, and solutions as well.

I think the silver turns black as it oxidises, just like copper turns green. I used to clean the silver with toothpaste. I guess it makes sense that the toothpaste could be used that way, since it cleans stains on your teeth.

I was brought up in the south with silver and learned that the conditions around it make it almost impossible to avoid the impact of the entire world around it, indoors or outdoors. After learning the pain of caring for it, a dear friend who worked in a store that sold silver advised me keep it away from air. period. put it in a location wrapped up in something around it to keep it away from the air around it, or plan to clean it over and over again. If If you put it in a good silver box or container it may keep the mess out for a while but just not displaying it in any way and taking it out to look at or use and run it back into hiding and it probably can avoid the condition for a while if you keep it closed in.

When I was a kid one could smell and taste it but now they treat the water with hydrogen peroxide which gets rid of the sulfur smell and taste but not the sulfur itself.

Check the dishwashing detergents for sulfur too.

Maybe I will switch to Ivory unscented and see if that changes things.

the 5 different tap water cities I have lived in in Texas to clean, oxidation has never been a problem. My
everyday flatware goes in the dishwater with no problem. Only use the real stuff for special. Although every once in a while a piece of the real stuff sneaks into the dishwasher with no lasting effect.

So that's not the cause/.

The "real stuff" for someone who has been keeping house as long as I have is often a jumble of old silver plate sets and now worthless as a set

I do have a few pieces of the REAL real stuff (which is sterling) but that's not in daily use.