I ended up using a simple float switch. Since my sensor is battery powered I wanted something very low power. I ended up using a panStamp which is like and Arduino pro mini with a radio transceiver built in. I set it up to sleep for 8 seconds, wake up, check the level, transmit the status then go back to sleep. The whole thing is attached to my skimmer cover. I also added an accelerometer and set it up for low power setting. I did this so the sensor would know when the cover was not in place. I didn't want it to send out a low water signal when I removed the cover to clean out the skimmer basket. I'm using a CR123 battery and the voltage drops about 1/100 volts per day (the panStamp is also transmitting the battery voltage). So that's not bad. The panStamp does have a different sleep mode which uses even less power. Also the accelerometer is powered all the time, even though it doesn't use much, I could probably power it with an output pin, only turning on power to the accelerometer when I wanted to check it.
I attached a couple pictures of my setup.
