If your windows look clean while wet and hazy once dry, the problem is almost certainly your water, not your technique. Penang tap water carries dissolved calcium and magnesium. When that water evaporates on glass, the water leaves and the minerals stay, and what you see is a thin mineral film sitting on the pane.
Why more scrubbing makes it worse
Because you are not removing the minerals, you are redistributing them. Wiping a dried mineral film with a cloth and more tap water dissolves some of the deposit, spreads it across the pane, and then leaves it to dry again — with a fresh layer of minerals on top from the water you just used. Each round adds a little.
What purified water changes
Running water through filtration and a de-ionising stage strips the dissolved solids out. What lands on the glass is water with effectively nothing in it, so when it evaporates there is nothing left behind to see. This is why we can clean upper glass with a pole and simply let it dry — no squeegee needed, no streaks.
Where the detergent comes in
Purified water dries clean, but it will not shift a greasy film on its own, and Penang glass collects plenty of it — traffic film, coastal salt, cooking grease. That is what our own blend, Lye's Window Juice, is for: a mild pH-balanced surfactant that releases the film so the water can carry it away, then rinses off completely instead of drying into a haze of its own.
On reachable glass we still finish with a squeegee and a hand detail on the edges. Not because purified water needs help, but because a blade lets us see the pane as we work and the edges are where any missed spot shows first.
The rubber nobody thinks about
A squeegee blade dulls after roughly twenty windows. A dull blade skips instead of pulling water cleanly, and skipping leaves the fine lines people call streaking. Changing rubber on a schedule rather than when it visibly fails is one of the least glamorous and most important parts of getting a consistent finish.
What you can do between visits
Wipe with distilled water if you want a genuine improvement on small panes, and squeegee your shower screen after every shower. Mineral staining on glass only forms when water is left to evaporate on the surface, so removing the water removes the mechanism. Fifteen seconds a day prevents a RM200 hard water removal job later.
Want it done properly instead?
Window cleaning in Penang starts from RM100, with purified water on every job and both guarantees included.