[magic1]

Been doing this house for over 2 yrs. Lasat 2 visits custie says they dont dry as good as they used too. I put it down to the house 2 doors up having work done and the dust and stuff blowing over sticking to wet windows.

On my last vist on close inspection found stained water marks on glass even after i trad them. They seem to be coming out the wall dripping over glass and stainig them. uPVC also got a line of yellow stain too. Running down in lines.

Any clues on what it is and how to get it off?

[ftp]

Mineral deposits from the wall i.e. calcium. I've got a few where they have stone lintels above. Mineral deposit remover or limescale remover will get it off temporarily. 

[magic1]

ok thanks.

[jouk45]

this stuff should get it of the glass, well recomeded by many w/c
http://www.windowcleancentre.co.uk/productdetails.aspx?ProductID=185&SectionID=40

[NWH]

You sometimes get this if the gutter is broken and water constantly drips down onto the glass,try ettorre mud that should shift it that`s what i use on glass like that.

[wfp master]

could be salt coming out the stone or brick work saw that a few times on sandstone buildings.

[Londoner]

Its run off from the wall. Windows should really have a skirt above them to prevent this happening but rubbish builders don't bother putting them in. Seen it a lot with new extensions.