I'm not sure what "sour" means. If it's gas water heater, you could have a small leak. Or you might have an unvented drain. These are common in homemade plumbing jobs put in for basement bathrooms like all those that homeowners brag about having done without a permit.

Okay, that is the only way I can describe the smell: mild sauerkraut smell. If I keep the door to the water heater open the smell is not as strong and barely noticeable so maybe the "unvented drain" may be the problem. Is there a way to vent the drain now?

One person's sauerkraut is another person's formaldehyde! That's the gas usually put into odourless natural gas so leaks can be obviously detected.

If you're on natural gas, you should be able to get the supplier to check for you if that's the source. I would do that promptly.

If your sauerkraut is sewer gas, you could have a faulty trap in the shower, no proper venting or (and this doesn't seem likely from your descrioption) a floor drain in the basement that is going dry.

Hi, thanks for the suggestions and sorry it took me awhile to get back....

First the smell is coming from the drain. Now what does it mean for a drain to go dry? I thought we had just septic but there may also be a grey water system... The washer and utility sink seem to drain into a pipe next to the drain in the floor... Could the drain be clogged because of this? The waste pipes (which seem to also drain shower water) goes to the other side of the house. Would a septic system be setup like that?

So I guess I am wondering is this drain connected to the septic and something is clogged or would this drain simply drain into its own field?

So I guess I will check the going dry theory and see what happens, thank you!

So taking a shower or doing laundry brings on the smell whereas before it didn't? Water is being sucked out of the trap. If there have been no other changes to the plumbing, the most likely cause is a clogged vent.

A Shower never affects the smell, doing laundry did but I do not know if it was after washing or after drying or the process together. The duct work for the dryer runs through the water heater closet. The duct work was not properly attached so we put in a new dryer duct and insulated it so it would no longer heat up the area.

After I figured out what a dry trap/drain was I poured 4 gallons of water in the drain... the smell subsided... tomorrow I will pour more in and with the weather being warmer I can air out the room and the garage to which it exits and then I will do a load of laundry to see if it comes back. Nothing drains into this floor drain so I could see where the water in the trap could evaporate especially being heated by the dryer.

I so far cannot find the vent that is attached to this drain to see it is clogged... Any suggestions on where I might find the vent? thank you....

We no longer have the smell after a shower or it was coincidental to the us doing laundry.... my apologies for not correcting our original assumption!

Nothing drains into this floor drain so I could see where the water in the trap could evaporate especially being heated by the dryer.

That's probably it.

New houses will usually have a plastic drip tube from some nearby water source--even a high-efficiency furnace or central AC--to floor drains to keep the traps full.

I read somewhere recently in a history of plumbing that it took a couple of hundred years for someone to come up with the idea of a trap so toilets could be moved inside homes. Heck, I grew up in the '50s in rural Ohio and outdoor privvies were still in use. That's what I had at my cottage in the '90s--an incongruity with satellite tv etcetera that guests (and my ex) weren't all that happy with.