I just sent my husband to the emergency room with an open wound on his hand from the power washer he was using to wash the garage. There wasn't any bleeding but his arm got water inside. Is this a serious injury?
Power washers can put out a stream of water with enough force to cut open the skin and even damage underlying tissue. There has been at least one report of a tendon and nerve laceration from this very type of injury.

If the stream of water is set at a high enough pressure, the force of the spray coming in contact with any part of the body can cause considerable damage. Water forced through the opening in the skin and into the soft tissue can result in a compartment syndrome.

Compartment syndrome is caused by swelling in an area that can't expand very much. The tight connective tissue over soft tissue can spread a little to accomodate mild to moderate inflammation or edema. But there isn't room for a large amount of fluid. Immediate treatment to remove the fluid is needed to avoid serious damage.

Once the fluid has been taken care of, the hospital staff will probably keep your husband for an extra hour or two for observation. If necessary, the on-call surgeon can be brought in for emergency surgery. Otherwise, he will be followed up by his own personal physician.