Compressed air always contains water -- it's physics, not a fault. When warm air is compressed, the moisture condenses as the air cools in the tank. If the tank isn't drained regularly, water accumulates and eventually gets carried into the air lines. The fix is simple: drain the tank daily.

What you'll see

Water sputtering out of air tools, spray guns, or blow nozzles. Rust forming inside the tank (you may see rusty water when you do drain it). Water pooling at low points in the air piping. Paint jobs ruined by water spots. Pneumatic tools losing performance or rusting internally. When you finally open the drain valve, a large amount of water comes out -- sometimes more water than air in a neglected tank.
Before you assume this is the problem

If you're draining the tank daily and still getting excessive water, the amount of moisture may be normal for your conditions (high humidity, heavy use) and you need additional equipment: an aftercooler, water separator, or air dryer. See: No Point-of-Use Filtration, High Humidity Environment.

How to diagnose

  1. Open the tank drain valve

    Open the drain valve at the bottom of the tank. If a significant amount of water comes out, the tank hasn't been drained recently enough. Some tanks can accumulate liters of water per day in humid conditions with heavy use. A small compressor in a humid workshop can produce 3-5 liters of condensate per day.
    Result: No water = tank is being drained adequately. Significant water = needs more frequent draining.

How to fix it

  1. Drain the tank at the end of every day

    Make it a habit: at the end of each work day, open the drain valve and let it blow until no more water comes out -- just air. Leave the valve cracked open overnight to let any remaining condensation drain. Close it before starting up the next morning. This single habit prevents most water problems in small shop compressor systems.

  2. Install an automatic drain valve

    If manual draining gets forgotten, install an automatic condensate drain on the tank. Timer-operated drains open on a schedule (e.g., every 15 minutes for a few seconds). No-loss drains use a float mechanism that opens only when enough water has accumulated. They cost $50-$200 but eliminate the daily task and prevent tank corrosion.

  3. Check the drain valve itself

    If the drain valve is hard to open, corroded, or won't close properly, replace it. A valve that won't close leaks air. A valve that won't open traps water. Replace with a ball valve for easy operation -- the original petcock-style valves on many compressors are small and clog easily.

Common mistakes

The most common mistake is never draining the tank at all. I've seen compressors where the tank was half-full of water and completely rusted inside. This is dangerous -- a corroded tank can fail under pressure, which is catastrophic. Also: don't just crack the drain for a quick pssst and call it done. Open it fully and let it blow for 10-15 seconds until only air comes out. There's often more water than you think.

Parts & tools

Replacement drain valve or ball valve (if original is corroded). Automatic condensate drain (optional but recommended). Thread sealant tape.

Review safety precautions before starting →

Safety

Open the drain valve slowly. The tank is under full pressure and the water/air mixture will spray out forcefully. Point the drain away from people and equipment. Wear eye protection.