  Water maser polarization observations in the precessing jet of W43A have
revealed that it is magnetically collimated. Here we present a detailed
description of the physical properties of the water maser environment in the
jet. We discuss the maser saturation level and beaming angle as well as the
intrinsic temperatures and densities. Additionally, we show that the
polarization angle of the strongest red-shifted maser feature undergoes a fast
rotation of 90 degrees across the maser. Along with the variation of linear
polarization fraction, this strongly supports the current theoretical
description of maser linear polarization.
