Would it devastate me financially to get that $1800 bill for replacing a hot water heater ?

If not in the city, and not in the ETJ, then it's a lot easier, provided you can get water (probably need to drill water wells so thats a separate ground water district) and sanitation (some sort of onsite sewage treatment).

I just sold one of my OREO in Jackson MS.. 1 year ago as a vacant house needed full rehab I might have gotten 25k from a local for it.. just went into contract last week with a hedge fund for 71k NET to me they pay all costs and back tax's.. so something is in the water. 

Borrowers many times especially if they are newer actually have no clue as to how bad it can be with these investor friendly lenders if you have a water landing..

How is water split? 

If the landlord is paying any utilities that are based on usage such as water, then I might discuss a rent bump to compensate for the anticipated increase in usage and address that with the lease update adding the person as an occupant. 

My water usage bill is the same.

We are having our roof replaced due to storm damage, however, when the shingles were removed another storm came through the area and caused a significant amount of water damage inside the house.

When we stopped finding good deals about 5 or 6 years ago, we just started throwing every penny into paying down the principal across our fleet (paying off higher interest rates first, obviously).Looking back, we probably should have invested that money in the stock market because our interest payments were about 4 or 5%, and we could have doubled that with fairly safe stocks, but that's water under the bridge I guess. 

I added a decent amount into the house (new paint, new hot water heater, brand new kitchen, better layout) but I’m not sure if that’s enough for me to appraise for 20% equity.