The Kärcher WD 4 S V-20/5/22 is very similar to the WD 4, but it's made of stainless steel. The advantage of this is that the vacuum is less sensitive to water and wear, which increases the lifespan. The vacuum has a 20L tank for both dust and liquids. That's useful, because you can use it for the most diverse jobs this way. Don't feel like buying new dust bags every time? No problem. The device also works fine without a dust bag. You can empty the container after use and get on with your work. When the filter is full, simply rinse it under the faucet. This way, you don't have to buy a new one every time.