How can I force HomeKit to send me a SMS/Notification alert (or email) if the basement floods? I use HomeKit to simplify home management for the elderly.  One of the things I want to address is the failure of a sump-pump, or flooding condition. 

Is there a way I can cause a HomeKit sensor to cause this notification?
It depends on the manufacturer of the sensor you're using. If it supports HomeKit notifications, you can set them by pressing on the device's icon in the Home app.