If your double kitchen sink is backing up, there is likely a clog in the drain pipes. Here are some possible reasons why this might be happening:

1. Food particles and grease: Over time, food particles, cooking grease, and other debris can build up in the drain pipes, causing a clog.

2. Foreign objects: Items such as utensils, bottle caps, and pieces of plastic can accidentally fall into the sink and lodge in the pipes, causing a clog.

3. Low water pressure: A poor flow rate from the faucet may cause debris and dirt buildup in the drain pipes.

4. Improper installation: If the pipes are not properly installed or have corrosion, water and debris will not flow evenly from both sides and eventually clog the pipe.

To troubleshoot, first, try clearing the clog with a plunger or drain snake. If this doesn’t work, you may need to call a plumber to diagnose and fix the problem. A plumber may perform a camera inspection to see if there is a problem further down the pipe or recommend hydrojetting, which involves using high-pressure water to clear out the blockage.