The answer to 'why is my water line won't flush' is that there could be a blockage or obstruction in the water line preventing proper flushing. This could be caused by a buildup of debris, mineral deposits, or a physical obstruction like a tree root. Symptoms may include slow draining, gurgling sounds, or complete loss of water pressure.
To troubleshoot, you can try plunging the toilet or using a drain snake to clear the line. If that doesn't work, you may need to call a professional plumber to inspect the line and use specialized equipment to clear the blockage. They can also check for any other underlying issues that may be causing the problem.