[seamus campbell]

As above, why do window occasionally streak and how to avoid it.

many thanks

[Griffus]

Are you sure this isn't between the panes. Lots of double glazing has this issue, including new units. Tends to only be visible in the sun.

[seamus campbell]

no i  think its on the glass, this is obviously only on trad, am i using to much detergent. how soapy do you have your glass

[G Griffin]

You're not breaking down the dirt/grease well enough to squeegee it all away.
Spend a bit longer with the applicator on the window. Or wipe the window first with a wet/damp microfibre before soaping up.
This not only helps clean the glass but also aids squeegee glide by wetting or cooling the glass.

[Tom White]

Are you using decent quality rubbers and changing them often enough?

[Harry Robins]

Got to agree with the above answer, probable culprits worn squeegee rubber or not enough water used on glass

[dannymack]

not fast enought with the squeegee the sun is drying the soap to quick. dont use to much soap in ya water !!!