We have a WaterCop system at home from the ancient days before Apple HomeKit and also an old lighting system. The first one has false alarms and we can't ever tell which sensor actually triggered since they all feed a single sensor into the alarm system.
The lighting system has failing switches so things like outdoor lights don't go on. That thing must be 20 years old by now.
We've been waiting for HomeKit to mature as it seems to be very safe (as an aside, Ring seems just so scary, with enablement of warrentless search so any Ring feeds can go right to the law enforcement without any warrants), so having something which is privacy first is going to be more expensive (than say the bottom dollar Amazon systems like Ring, Blink and Echo) and also less capable (as they don't collect samples from you like Google Home).
But the problem is that of the big three, Apple is definitely the smallest and we are the knee of the curve for implementation with Thread and now Matter just about to arrive to improve interoperability and widen the hardware set.
Reliability and WiFi vs. Zigbee vs. Thread
The main issue with all these devices is reliability particularly those that are WiFi connected. For instance, our WeMo smart plug are WiFi connected and they always seem to be offline. The Satechi smart plug is slightly better. The Vocalink do not work at all. Also, I do find that the Hue (which uses its own Zigbee hub) does have light bulbs that disappear. The hope is that a new standard Thread will work better and the operating system on top Matter (when it comes out) will be even better.
Now Eve has been aggressive about moving to thread, but sadly my two Eve devices, a Smart Water Controller and the Eve Room are not Thread capable, they use WiFi. I've actually found the Eve Room to be OK, but the micro-USB connection is unreliable so even though it is plugged in, it will still discharge. I don't know about the Smart Water controller as I've not had a chance to deploy it.
But, if you can't wait for Matter (which is supposed to arrive next year), then what can you do? Well for light switches and water sensors, the very first Thread-enabled switches like the Eve Light switch and the Eve Water Guard are starting to show up, but I'm not sure I would rely on them for something as "it must work" as an in wall light switch.
- Eve Water Guard. If you are on the bleeding edge, Eve seems to have thread enabled and HomeKit enabled products. But the Eve Water Guard speaks Thread which means that it can theoretically talk to a HomePod mini which is a Thread router. No word on how interoperable it will be with Matter and I'm sure no one knows. The other drawback is that is it wired so it needs the power to be working (but it doesn't require battery changes which is nice). It's $99 on Amazon. The cool thing is that the cable stretches a long way so it is not a single point sensor, so you can lay it around your basement machine room for instance. Each 6.5 foot length is another $20 so it does get costly, but it is better than lots of sensors separately.
- Aqara Water Sensor is the only available HomeKit system that uses Zigbee so it needs an Aqara hub which is a pain. The other choice is a non-Thread device but one that is pretty reliable for water sensing (and cutoff). The Fibaro has integration with a water cutoff valve which is what you really want. The main problem is that it is bluetooth only so you need your iPhone or an AppleTv or HomePod in range. That's kind of hard in a basement or other place. I'm trying to build an alarm system that is just HomeKit with Aqara so this is a good piece to experiment with.
- Lutron Caseta. They seem to make the most reliable HomeKit Light switch right now. Also unlike the Eve Light switch which is European only and doesn't fit into a standard junction box, this does. It does need its own hub though. There are other ones out there, but I'm not sure I would rely on WeMo as an example given my personal experience with the SmartPlug. YMMV. $99 from Amazon and this includes a bridge and $59 per switch at Amazon.