(2) Wear of cylinder, piston and other parts, due directly to the fact
that water is a bad lubricant, and as the density of water is greater
than that of oil, the latter floats on the water and has no chance to
lubricate the moving parts.

(3) Wet air arising from insufficient quantity of water and from
inefficient means of ejection.

(4) Mechanical complications connected with the water pump, and the
difficulties in the way of proportioning the volume of water and its
temperature to the volume, temperature and pressure of the air.

(5) Loss of power required to overcome the inertia of the water.

(6) Limitations to the speed of the compressor, because of the liability
to break the cylinder head joint by water confined in the clearance
spaces.

(7) Absorption of air by water.

Before the introduction of condensing air receivers, wet air resulting
in freezing was considered the most serious obstacle to water injection;
but this difficulty no longer exists, as experience has conclusively
demonstrated that a large part of the moisture in compressed air may be
abstracted in the air receiver. Even in the so-called dry compressors a
great deal of moisture is carried over with the compressed air, because
the atmosphere is never free from moisture. This subject will be
referred to more fully when treating of the transmission of compressed
air.