We purchased a new home in January that has a well and they had to do some work on the well before we bought it. We had a water softener installed because of a lot of hardness but were told that the iron level was minimal so we wouldn't need an iron filter. We have been in the house 2 months and a few days ago we started noticing a greasy smell when we did the dishes and then the next day in the shower. I also noticed a slight film in the toilet tank so suspected iron bacteria. We had the water softener guy come out and look at it. He started with the cold water and we couldn't smell anything so I ran the hot and it took a minute for the smell to come. I took him upstairs to look inside the toilet tank that I had not cleaned of the rust when we moved in and left the cold water running downstairs. My husband came in and turned it to hot because that is where we noticed the smell so I turned it to cold again explaining that the water guy suspected it was our hot water tank. He took us to the basement and showed us how to shock the hot water tank the entire time I left the cold water running. There was a very faint smell the same in the water softener salt receptacle but hardly noticeable. When he left I was still running the cold water and a few minutes later the greasy smell came - figures. So we did the test in the cold water taps before we went to bed upstairs and it took 3-4 minutes before we could smell it but we can smell it almost instantly in the hot. This morning I ran the cold water tap in the guest bathroom as it never gets used to see if we were smelling leftover from the hot water in the other taps because we use them a lot more. After 3-4 minutes I still couldbn't smell anything. I have also heard that the sacrificial anode in the haot water tank might need to be replaced. Any advice. Desperate new home owner.

You said the home was new but I take that to mean new to you. How old is the building and do you know the age of the water heater? When the anode goes your water smells like a rotten egg, any chance that's what you smell?

What kind of piping do you have? Both to the house from the well and down the well?

I also noticed a slight film in the toilet tank
That plus the greasy smell bothers me. You could have intrusion into your well. Who knows from where or from what. I would take the water into The Health Department and have it tested. Let me know what they find. Good luck, Tom