There are several things that could cause this. You should examine your bill closely, as in "look at the details, not just the amount at the bottom."
You could be using more water in the winter... why this would be true, I don't know, since I don't know your habits. Maybe you shower more, or longer, in the winter. Maybe you let the water run longer to warm up in the winter.
Alternatively, the rate may have gone up, and it may be unrelated to winter.
The cardboard could cause a backup of the sewer. Eventually the cardboard will break down and dissolve.
Only if your drinking the contents otherwise, no.
No, something more basic is the cause of that.
Damage must be due to a covered cause for the damage to be claimed on your homeowners insurance. I cannot think of any way damage to a sewer could be from a covered cause.
Yes, it contain methane.
Perhaps. But usually hepatitis is caused by a virus or a bacteria.
A sewer system is the sewer or the sysyem of the sewer.
Either you have a blockage present or your vents on your sewer lines have become blocked or you need to install more vents.
You kiddin, right? Cause these are not answers. Just ramblings.
Oh Yes, very common problem
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sewer gas. either your trap has run dry from lack of use or is improperly or not vented causing your line to syphone. this will cause the water in the p-trap to syphone out allowing the sewer gas to ecsape.