Water coming out from your air compressor is far from a good thing.

Not only can it damage an otherwise quiet compressor, but also the tools you use. Not to mention making it harder to operate those tools!

The first solution is to drain your compressor. Turn it off, reduce the pressure, and drain out the water. To prevent build up in the future, use an air dryer (or air filter) to minimize the moisture in the air you use. More details on all of these water-compressor issues below.

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Why is there water in the compressor system?

Basically, your compressor is drawing in air from it’s surroundings.

And there’s a TON of moisture on the air.

So what happens when all that air is compressed? It condenses. It creates water.

Do you know one thing that’s bad for your tools? Water!

Not only the degradation of tools, but issues in operation, too. Try spray painting when your paint is getting diluted because of water in your system. It just doesn’t work.

Did you know – a 200cfm compressor can typically produce up to 18 gallons of water a day!

How to drain water from your air compressor

Every air compressor has a basic solution to water – a drain.

For the unfamiliar, here’s a quick step-by-step to using the drain:

  • Turn the compressor off. Make sure it’s completely switched off, and ideally unplugged.
  • Reduce the pressure. We don’t want air bursting out the drain. Use the safety valve to reduce the pressure until it’s less than 10 PSI.
  • Prep for water. Find the valve (on the bottom of the tank) and, if necessary, place something underneath it to catch the water.
  • Open the valve. Just open it slowly and allow the water to drain out. Once done, tip the tank at a few angles to encourage every last drop to come out.
  • Close the valve. Use the compressor as standard again. This may seem a no-brainer. You’d be surprised how many people forget this, then wonder why their pressure doesn’t build up afterwards!

It’s sometimes asked if the valve should be kept open when you’re not using the compressor – to keep it empty. In my opinion, this isn’t worth the risk of insects bringing in dirt and making your compressor their home. Just quickly drain before you use the next time.

If your drain is in a difficult spot to reach, you can get drain extension kits to draw the valve point out and make it easy to reach (meaning you’ll drain it more often, which is better for your compressor).

Don’t want to deal with this manually?

There’s such a thing as automatic tank drains.

These hook up to the compressor and drain the tank following a certain trigger. Generally, this is when the compressor is turned off, or even right after every burst of air.

Automatic drains not only save you hassle, but they help your compressor last longer – by preventing a greater build-up of water and rust.

An automatic drainer like this one from Zijia can save you on hassle and extend the life of your compressor.

How to prevent water in an air compressor

Now that we’re working with a dry(er) air compressor, let’s talk about how we can keep things that way.

This Solberg is one of the most popular compressor air filters on the market. 

1. Air Filters / Separators

The most basic weapon against water is to filter it out using a simple air filter.

There’s a ton of water in the air, and we want to make that minimal.

An air filter will clean the air and pull out some of the water that’s in the line so it doesn’t go directly to your tools.

These are cheap, simple tools that will quickly pay for themselves in maintenance savings. However, their effectiveness is fairly limited.

2. Dry The Air.

If you have a quality air compressor and want to fully protect it, a refrigerated air dryer is the only way to go.

These are more costly than a basic air filter, but for good reason.

One of the most popular dryer combos – the PneumaticPlus SAU430-N04DG-MEP Three Stage Air Drying System.

Instead of a basic filter system, an air dryer will actively cool the air down to a much lower temperature (say 40F). This causes the air to condense and release much of its moisture.

This water is quickly collected and drained out.

The now-dry air can be passed into the tank and through the pipe system with zero chance of it condensing. The lower temperature means it’s pressure dew point is far lower (even down to -40F!).

On top of this, they are often combined with air filters and pressure regulators – like in the example above.

3. Oil It Up

Truth is that you’re gonna get dirt in the line. And, you’re gonna get a little water in the line, too.

To help, make sure to put a little bit of oil in the tool inlet. Just turn the tool upside down and put a few drops of oil in the inlet.

This keeps the tool intake lubricated, and helps to prevent dirt or water from getting into the tool itself. .

4. Open The Drain (A Little)

This isn’t something you should do all the time, or even if you’re unsure.

If you’re using a water sensitive tool (like a spray paint gun or a sandblaster) then it might be worth opening the drain a little bit.

With the drain slightly open, any water built up will be seep out and keep the air extra dry.

This will cause air to look out and put much more demand on your compressor. This should only be done in certain situations and monitored with care.

Frequently Asked Questions

What is Pressure Dew Point (PDP)?

To understand water in an air compressor, you need to understand the pressure dew point (PDP).

Simply this is the point (temperature) when vapor water saturates and starts condensing into liquid.

This accounts for the pressure that the water vapor (or any gas) is under. The PDP changes as the pressure changes.

To minimize water levels, we need to minimize the PDP.

What affects the Pressure Dew Point??

This is a good question. Some climates will cause your compressor to seem like it’s drowning within a few hours, while others almost never have an issue.

All the factors are related to the air itself.

  1. Intake Rate. Air contains moisture, and the more air we take in the more moisture we take in. A higher intake rate (in CFM) means a higher water content in the system.
  2. Relative Humidity. This number is the percentage of saturation in the air relative to the maximum it can handle at that temperature. The wetter the air, the more water we get.
  3. Temperature. The warmer air gets, the more moisture it can hold. This is why hot climates can get so humid, but cold climates are often dry.
  4. Pressure. Think of pressure like squeezing a sponge – the more you squeeze, the more water comes out. In other words, the more air we pack into a contanier, the more the water seperates out (since the air can’t hold it).

Want an estimate for your compressor? There’s a great calculator over at AtlasCopco.

What harm does water do?

Water can harm our tools and systems in a lot of ways. Mostly these happen gradually over time – they may not be noticeable until damage is done. Some examples include:

  • Corrosion of the equipment and/or piping system
  • If it’s ice-cold, water may freeze and expand inside the system.
  • Many issues with spray paint – diluted, color changes, harder to apply.
  • Issues with pneumatic controls which are hard to repair.

The best way to avoid the issues is to prevent them from happening – using our tips above.


Water in such an important can cause a ton of worry.

I hope this article’s helped you get a bit more familiar with draining and preventing water buildup in your air compressor.

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Thanks for reading, and have a great day.