Item 2 seems like the simplest / cheapest to tackle. There are a few threads on here regarding level monitoring for various applications (pools, Christmas trees, etc.) - here’s one “hacky” way to do it:
Several threads recommend the Aeon sensor over any leak sensor because it’s designed to work as a wet or dry sensor, so it won’t burn through batteries constantly reporting if it’s typically submerged.
https://www.amazon.com/Aeotec-Water-Sensor-Z-Wave-Flood/dp/B00H3TJ3P4/ref=sr_1_1?s=hi&ie=UTF8&qid=1517494949&sr=1-1&keywords=aeotec+water+sensor+6
In the industrial direction, you could just connect a few of these to dry contacts on contact sensors. They have NO/NC outputs and are 120VAC rated - so for example, if you were using a pump to fill the tank, you could have SmartThings switch on an outlet when city water comes back on, and use a float switch at the top of the tank to turn the pump on and off to keep the tank topped up.