1. Beyond the Cowl: The water could be entering *before* it reaches the cowl. Check these areas:
* Windshield Seal: This is a very common culprit. Carefully inspect the entire windshield seal, both inside and outside. Look for cracks, gaps, or areas where the sealant has deteriorated. A small crack can allow significant water entry. You might need a professional to replace the windshield if the seal is compromised.
* A-pillar Seals: The seals where the windshield meets the A-pillar (the metal post between the windshield and door) can also leak. Examine these closely for damage or gaps.
* Weatherstripping around the door: While less likely to pool directly on the floor, a severely damaged door seal could allow water to run down the door and into the interior, potentially explaining a floorboard puddle.
2. Inside the Cab:
* Drain Holes: Even with a sealed cowl, clogged drain holes can cause water to back up and overflow into the cabin. Check all drain holes within the cowl and firewall for clogs. Use compressed air or a small wire to clear them.
* Firewall: Water could be leaking through the firewall itself. This is harder to diagnose but could involve rust or cracks in the firewall's sealant. Inspect this area carefully, paying close attention to any seams or penetrations.
* Sunroof (if equipped): If your Silverado has a sunroof, check its seal and drainage tubes for clogs or damage.
3. Systematic Approach:
To pinpoint the leak:
* Water Hose Test: Have a helper slowly pour water onto the suspect areas (windshield, A-pillar, etc.) while you watch inside the cabin to see where the water enters. Start with the most likely sources.
* Visual Inspection: Thoroughly inspect the entire exterior of the truck, paying close attention to any seams, joints, or openings. Look for rust, cracks, or signs of previous damage.
* Interior Inspection: Carefully examine the interior, looking for signs of water damage beyond the puddle. Discoloration, mold, or mildew can indicate a persistent leak.
4. Professional Help:
If you've tried these steps and still can't find the leak, consider taking your Silverado to a reputable auto repair shop or a specialist in automotive water leak repair. They have the tools and experience to diagnose and repair even the most stubborn leaks.
Remember safety first! When working on your vehicle, always disconnect the negative battery terminal to avoid electrical shorts.
