Toilet/sink/bathtub/shower frequently breaks

It is normal for the frequency/number of uses to affect how often an item breaks, but it should break less often with certain upgrades (sturdy faucets, superior flush, etc) than without. More expensive items with higher reliability scores should also break less (ie more uses before it breaks) than similar items with lower reliability scores.

Are you sure your goofball sims aren’t autonomously pranking the toilet?

I'm also having issues with appliances breaking. I have fixed the same bathtubs, sinks, and toilets about 6 times in the same Sim week because every second I look, they're broken. This has been going on for a couple generations in game and it has definitely gotten a bit annoying. Mine is in a bigger house as well, the Ward household in Del Sol Valley. It actually made me get the 10 broken objects achievement because I didn't realize I needed to fix every. single. plumbing object in my house.

I thought of taking proper notes on the frequency for better reporting, but somehow my bathroom no longer break frequently as before. Currently I only have 3 sims in my household and the bathrooms (all upgraded) only broke down once in 1 sim week. Previously I had around 5-6 sims in the household and my bathrooms would broke down every 2-3 days.

Regarding goofball prank and reliability, I stopped playing with Kim-Lewis household once Olivia (goofball) aged to teen, and her mischief was at level 2. I doubt she or other sims doing it as when I don’t instruct them to do anything, they either went straight to fireplace to keep warm or go swimming. And no one in Goth household have goofball or other mean/evil traits. 

I checked both Goth and Kim-Lewis household plumbing stuffs reliability, lowest is 5, highest is 8. And when I first played with the households (no upgrades), I would have 1-2 stuffs broken every 2-3 days. I now mainly play the Goth household, in the beginning, the bathroom sinks and toilets (all reliability 8) keep breaking down every 2-3 days. I upgraded all of them but I still need to repair them like 2-3 times a week (when I still have around 4-5 sims in the household). The difference was like, before upgrading, I would have one item in both bathroom broken, after upgrading, it was like only one item for the whole house.

I think I will make a new save in the future just to test how many times before somethings break for each reliability scale.