It could be an easy fix like this or a bigger problem depending on the factors at play (are the joists accessible, will it mess anything else up if you just jack it up and reinforce, is there water damage or structural damage to the foundation causing the sag instead of just old joists, anything else going on like a supporting wall or posts under the floor, wiring or plumbing runs involved etc.).

I’m new to the note investing space and want to start off with buying a partial note to test the waters.

@Anthony Vander Meer Does the rent include electricity, heat or hot water?

House hacking is one of the most risk-averse residential investment strategies and will allow you to test the waters and strategically plan from there. 

The classic blue cities, SF, LA, Seattle, NYC, Boston are all the best deep water ports in America. 

To address these issues, the lot needs to be properly sloped to divert water away from the building.

If you had to come out of pocket for a water heater for $1,000 in a given month, or a $300 plumbing call, or an AC call, can you comfortably do that type of thing with your finances?  

One thing that got me was the age of the water heaters.

They'd be way better, unfortunately society works the inverse therefore they'll always be under water.

Some areas and lots use well water others have city water.