The short answer is: it depends. While a power washer can be highly effective, using it incorrectly can permanently damage your furniture. Urban outdoor furniture—often made from materials like powder-coated aluminum, wrought iron, teak, or synthetic wicker—requires specific care.
For durable, non-porous materials like aluminum and wrought iron, a low-pressure setting (under 1,500 PSI) with a wide 40-degree nozzle and from a safe distance (at least 12 inches) can be safe. Always test on an inconspicuous area first. However, for wood (especially softwoods), synthetic wicker, or furniture with faded paint or loose joints, a power washer is risky. It can strip finishes, splinter wood, force water into frames causing rust or mold, and irreparably fray woven materials.
A safer, recommended method is to use a garden hose with a spray attachment, a bucket of warm soapy water (use mild dish soap or a dedicated cleaner), and a soft-bristle brush. This combination provides ample cleaning power without the destructive force. Rinse thoroughly and let dry completely.
In summary, reserve the power washer for the most robust, solid metal furniture and always err on the side of caution. For most urban outdoor settings, gentle hand cleaning will preserve the beauty and longevity of your furniture far better.