This is a simple project I did to avoid adding water into my machine each time I take a cup of coffee. It's a pretty simple system but it also requires basic plumbing knowledge and electrical / soldering skills :-). This DIY will work with B40/B60/B70 model or maybe other if you have enough place for the small bracket and water level sensor that we'll see in a moment. Note: some suggested in the comments a mini plastic float valve http://goo.gl/fbu2Jt if its size fits your reservoir it might be a simpler setup (I did not test it).
Step 1: Ice maker maker tap valve kit
Tap Valve Kit
For 3/8" to 1" O.D. tube
Valve with 1/4" O.D. comp. outlet
25'x 1/4" O.D. polyethylene tube
1/4" O.D. comp. union
For installation of humidifiers, ice makers, and evaporative coolers