Is wireless an absolute requirement? If not, I have two suggestions, both of which utilize Berkinet's Phidgets plugin.
1) This option straight up uses a digital input on a Phidgets SBC: HC6000 Hi-Lo Sump Pump Controller (Dual Float Switch) - available on Amazon. daveHawk recommended this too and I like his overall solution. I've had this in place on a project with extremely dirty ground water for a couple of years and it's been working very reliably. Relatively inexpensive solution. I plugged a power supply into the HC6000's power outlet to drive a digital input on the SBC, which in turn (via Indigo triggers) turn turns on/off pumps. You can reliably use this device to drive a pump directly if the amperage isn't too high (completely removes Indigo from the equation). I suppose you could plug a z-wave device into the outlet instead, but you'd need to work out how the device behaves when it's receiving power vs. not (see daveHawk's recommendation for something elegant). If you go the HC6000 route, I'd recommend following the manufacturer's grounding technique. I was having issues until I implemented their suggestion. I've used this device successfully on a few projects, one of which has no computer automation whatsoever.
2) This is a 4-20mA solution (also available in 0-5V configuration) using a Phidget 4-20mA sensor board. This is NOT an inexpensive solution, but it's absolutely rock solid in its performance and has never required any maintenance in the few years I've been using them. It's a pressure transducer that reports back the depth of water in as little a 0.1" increments. Many manufacturers make pressure transducers, but I've had really good luck with Keller America Levelgage transducers. I fire triggers to turn on/off pumps and solenoid valves based on the level reported back to Indigo. This is quality stuff. I have all kinds of uses for the data returned, e.g., historical data on tank levels and volumes, etc., but it works great for the control aspect as well.
I don't want to badmouth any particular brands, but I work with companies that do big water utility stuff. One of them tried the Vegatronix products and they simply weren't up to the task. It might be for your application though.