
On exiting Dane Road Metrolink station, turn right (eastwards), down Dane Road. After about 700 metres, there's a footpath off to the left (initially north, then eastwards) (almost opposite Clarendon Crescent) through Priory Gardens and this will, in due course, take you across a big overbridge (over the M60 motorway) to Sale Water Park.
Attached leaflet may be of interest (although it's a little out of date, and assumes that you are travelling to Stretford Metrolink station, then getting a bus to Chorlton bus station, and starting your walk from there).
http://www.tfgm.com/placestogo/pdfs/Places-to-Go-Chorlton-Sale-ARCHIVE.pdf