For the person who has problems with water from the empty house next door:
1) Report the property to the Board of Condemnation. They will force the owner to make repairs:
2) Make sure the property is on DCRA's vacant property list (dcra.dc.gov). They will refer the property to OTR (Office of Tax and Revenue), and it will be taxed at the vacant property rate, which is significantly higher than the residential rate.
It ain't gonna happen fast, but they might have one less problem to deal with in a couple of months.