Research scope: This comparison uses Karcher’s current US WD chart. We did not measure suction or dust capture.
The current US WD choices
Karcher’s US lineup steps from the 4.5-gallon WD 3 to the 5.3-gallon WD 4, 6.6-gallon WD 5 P and 7.9-gallon WD 6 P S. The WD 4 and WD 5 P publish 78 and 76 CFM respectively; the larger models add reach and features rather than a simple “bigger is stronger” progression.
The WD 3 is the compact general-cleanup choice and includes a blower. WD 4 moves to an overhead flat-pleated cartridge and a 26-foot cord but omits blower and tool outlet. WD 5 P adds a power-tool outlet, adapter, blower and semi-automatic filter cleaning. WD 6 P S keeps those features in the largest steel-canister format.
A critical US-market warning
Karcher explicitly says it does not offer or authorize several similarly named models in the United States, including WD 4 P/S variants and WD 5 S or WD 5 P S. Those imports may not suit US power. Match the current US part number, plug and warranty rather than buying from the model name or foreign review.
Choose by debris and handling
For car, garage and ordinary wet pickup, hose reach, floor nozzle and ease of emptying can matter more than tank volume. A full tank of water becomes heavy. For a sander or saw, the WD 5 P/WD 6 P S outlet can switch the vac with the tool, but Karcher limits the tool outlet and total current; check the exact manual.
These residential units are not automatically rated silica extractors. Hazardous or very fine construction dust requires a vacuum and work method selected for the applicable exposure standard.
Buying route and verdict
Use Karcher’s current US WD comparison chart . Choose WD 3 for low-cost portability, WD 4 for the overhead filter and longer cord, WD 5 P for tool-trigger and filter-cleaning features, or WD 6 P S when the largest current canister fits the storage and lifting plan. Verify the US part number before checkout.