This is a project from several years ago, but it's still in use today and works quite well so I thought I'd post it.

There have been numerous simple projects out there where people have used a fish filter to provide a stream of running water for their cats to drink from. This goes one better by automatically refilling the water bowl as the water level drops. No more do you have to remember to add water or worry that when you're out of town for a few days that the cats (or dogs for that matter!) will run out of water.

Below you'll find the project outlined in pictures. There is no kit because this is such an old project.

Construction

Above you can see the whole assembly. The tupperware container that holds the water, the fish filter and cleans and circulates the water, the float switch and the water solenoid valve. The most hard to find part is the water solenoid. Here I've actually used a heavy-duty fluid control solenoid valve which I just happened to have lying around, but these are a bit harder to find.

You could probably use an ice maker solenoid valve. Say, something like this. The only issue you may have is the duty cycle on the ice maker valves is pretty low. ie they're only designed to be 'on' for a short period of time so may overheat in this kind of service. If you can find a valve rated for 'continuous duty', you should use that. If someone finds a good source of inexpensive continuous duty water solenoid valves, post it in the forum.

Top View

Front View

GFI Outlet powering the whole thing. IMPORTANT - Since you'll be mixing water and electricity with this, please make sure to use a GFI to protect anyone who might come into contact with this device!

Overflow reduction. Yes it'll still overflow, but with the reduced flow rate you've got a better chance of stopping it before something major happens.

Control switch wiring

Stabilization

Forum

Talk about it here