In reply to mcawle:
Washing detergents and softeners don't generally 'strip the DWR'. They, like DWR treatments, are surfactants, intended to change the surface tension of the water. DWRs increase the surface tension, causing beading, detergents reduce the surface tension, causing wicking.
Mix the two together, and guess what happens? Yes; they cancel each other out.
Traces of detergent can usually be removed by a pure soap wash, largely restoring the original DWR. But you do need to make sure your rinse water isn't then putting traces of detergent back, due to having a water path clogged up with lumps of caked-on washing powder...
Any mechanical washing reduces the effectiveness of the DWR, since it mechanically abrades the DWR from the fabric. This would happen even if you used a pure water wash.
Washing properly is generally good for a DWR, since it removes the body oil and dirt from the garment, both of which reduce the effectiveness of the DWR, causing wetting out.