#4 Drip, drip.
It’s the drain lines that cause heartbreak and despair. Leaks in the supply lines can't be ignored. A leaky drain line, seemingly too small to fix, will cause unimaginable damage over time. Sink drains, refrigerator drains, toilets, grease traps, cesspools, septic tanks, one of these will get you eventually.
I walked past the ovens in my kitchen and did a double take. Something was wrong. I stood back and sure enough the ovens looked rather lopsided against the back wall. They are kind of heavy, about 800 pounds or so. I dragged in a floor jack, lifted them on the low side and put in some steel shim plates to make them appear more level. A year later they had sunk again. They were sinking through the floor toward the earth as gravity would have it. Just a few drips an hour from the dish sink did this. I knew for some time something would have to be done but as the business runs seven days a week it was easy to ignore. The day the oven visibly fell three inches and threatened to take down the entire building we finally had to close. The repairs were extensive.
Hint; Plumbing is simple. Wettness is bad.