I cannot overstate the importance of finding a way to build a good rapport with your tenants as early on in the acquisition process as possible, as it will minimize or prevent countless headaches further down the road.When I took over my duplex with an inherited resident in one of the units, I had this conversation with the tenant prior to closing and found out that the toilet in their bathroom was clogging once or twice a week, and their shower head water pressure was super weak. 

Water pressure holds at the meter.

Older buildings, lots of water, insurance issues.

One of the restroom water pipes broke over the weekend and flooded the whole office that would need a major renovation.

I have checked the maps of the department of power and water and the location of the power line is highly inaccurate.

Before you spend any money, you just need to price everything out (i.e. cost of homes, moving costs, installation, hook ups such as electrical, water, etc). 

The apartment is inhabitable, just no water/toilet access.Luckily, the permit was issued by late Monday afternoon. 

Lots of old properties where I'm at, so it isn't unusual to expect $10k+ of capex out of the gate for water heaters, putting in central air possibly, and other old property issues.

Ran into some unexpected issues with having to run new power for the stove as well as having to run new water lines for the bathroom and kitchen.

Close proximity to another source of plumbing - either side by side, or stacked one on top of the other - means easier access to existing water and drain/vent lines, which will almost always be advantageous for your project budget.