You cleaned them last weekend. You spent twenty minutes with a cloth and a bottle of spray, and they looked brilliant. Then the sun came out and there they were again. Streaks. Smears. That infuriating haze that makes the glass look worse than before you started.
It’s one of those genuinely maddening household jobs. You do the work, you step back, you feel good about it and then the light shifts and you realise you’ve essentially just rearranged the dirt. You’re not imagining it, and you’re not doing it wrong. Well, you might be doing one or two things wrong. But mostly, there are specific, identifiable reasons why streaks keep coming back, and once you know what they are, the whole thing starts to make a lot more sense.
Why Streaks Happen in the First Place
Streaks are almost always a residue problem. Something is being left behind on the glass after cleaning and when light hits it at an angle, it shows up immediately.
The most common culprits are:
- Cleaning product residue – many spray cleaners contain surfactants or solvents that leave a thin film on the glass as they dry
- Dirty cloths or sponges – a cloth that’s been used before, even if it looks clean, can deposit old residue straight back onto the glass
- Hard water minerals – calcium and magnesium deposits left behind as water evaporates
- Soap that hasn’t been fully rinsed – a common issue when washing-up liquid is used without a proper rinse afterwards
- Polish or wax from previous cleaning products – these build up over time and become increasingly difficult to shift
The frustrating part is that some cleaning products actually make the problem worse with every use. They clean the visible dirt but leave behind their own residue. Over time, that builds into a film that ordinary cleaning can’t touch and you end up working harder for worse results each time.
The Problem with Most Window Sprays
Walk down any supermarket cleaning aisle and you’ll find dozens of window sprays promising streak-free results. Most of them don’t deliver. And there’s a fairly straightforward reason for that.
Most commercial window sprays contain added fragrances, dyes, or conditioning agents. These ingredients make the product smell pleasant and feel premium in your hand. They don’t help the glass. In fact, they’re often exactly what’s causing the streaks.
Ammonia-based sprays are a common example. They cut through grease effectively, which sounds ideal. But if the glass isn’t rinsed, which it typically isn’t when you’re using a spray-and-wipe method indoors, the ammonia residue dries on the surface and becomes a streak magnet.
Vinegar-based sprays have become popular as a natural alternative, and diluted white vinegar genuinely does cut through mineral deposits and grease without leaving a harmful residue. But concentration matters. Too weak and it doesn’t do much. Too strong and it can damage window seals over time.
Here’s the honest truth: the product matters less than the method. A basic solution of clean water and a tiny drop of washing-up liquid, applied correctly and rinsed properly, will outperform an expensive branded spray used carelessly. The fancy bottle is often the least important part of the equation.
Does Your Water Make It Worse?
Depending on where you live in the UK, your tap water could be a significant part of the problem and most people never consider this.
Hard water, common across much of England, particularly in the South East, East Anglia, and the Midlands, contains dissolved calcium and magnesium. When this water is used to clean windows and then allowed to dry, those minerals stay behind on the glass. The water evaporates. The minerals don’t. What you’re left with is a white, chalky haze that smears when you try to wipe it off and gets worse the more you fiddle with it.
According to Water UK, around 60% of the UK’s population lives in a hard water area. If you’re in Norwich, Cambridge, London, or anywhere across the Home Counties, this is almost certainly part of your window frustration and it’s not something you can solve by wiping harder.
The solution isn’t to stop using water. It’s to change how it’s used. Professional window cleaners like Simply Cleaning Services (https://simplycleaningservices.co.uk) use purified water that has had the minerals removed through a filtration process. This water dries completely clean, no residue, no haze, nothing. It’s one of the main reasons professionally cleaned windows tend to stay cleaner for longer than anything you can achieve at home with tap water.
The Cloth Problem
What you wipe with matters just as much as what you clean with. This is where most DIY window cleaning quietly falls apart.
Paper towels seem like a logical choice, they’re disposable, so there’s no residue from previous use. But standard paper towels break down when wet and leave fibres all over the glass. Those fibres catch light and look remarkably like streaks. You’ve essentially swapped one problem for another.
Old cotton cloths or T-shirts have a similar issue. They feel soft and harmless, but they pick up dust, lint, and old detergent residue from washing. When you use them on glass, you’re not just applying cleaning solution, you’re depositing whatever the cloth has been collecting since it was last washed.
Microfibre cloths are significantly better. The fibres are fine enough to actually lift residue from the glass rather than pushing it around. But they need a bit of looking after:
- Wash them regularly – ideally after every use on windows
- Never use fabric conditioner – it coats the fibres and kills their effectiveness
- Keep them separate from other cleaning cloths to avoid picking up grease or product residue
A fresh, clean microfibre cloth will produce results that are visibly better than anything else in your cleaning cupboard. The same cloth used five times without washing will actively make things worse. It’s one of those small details that makes a big difference.
Sunlight Is Working Against You
Here’s something that catches a lot of people out and it’s responsible for an enormous amount of window cleaning frustration.
Cleaning windows in direct sunlight, particularly on a warm day, is one of the most reliable ways to end up with streaks. The cleaning solution dries before you have a chance to wipe it off properly. The moment the liquid starts evaporating faster than you can work, you lose control of where the residue ends up. It sets quickly, and once it’s set, you’re essentially polishing something that’s already hardened onto the glass.
Professional window cleaners tend to work early in the morning or on overcast days for exactly this reason. The glass is cooler, the solution stays workable for longer, and there’s time to be methodical without racing the sun.
If you can only clean your windows on a sunny afternoon, work in small sections. One pane at a time, start to finish, before moving on. Don’t apply solution across three windows and then come back to the first one, it’ll already be setting.
Inside vs Outside: Different Problems, Different Causes
It’s worth separating inside and outside because the causes of streaking are genuinely different for each, and treating them the same way is part of why results can be inconsistent.
Outside windows are up against:
- Rain and hard water deposits
- Pollen – particularly brutal in spring and early summer
- Atmospheric dust and pollution
- Bird droppings and organic debris
- Algae and mould in shaded or north-facing areas
Inside windows are dealing with:
- Condensation residue, especially in kitchens and bathrooms
- Cooking grease and steam
- Fingerprints and skin oils around handles
- Dust settling on sills and ledges
- Pet nose prints, far more common than most people admit, and surprisingly difficult to shift
Outside windows often benefit from a rinse with clean water before any solution goes on, just to remove loose debris that would otherwise drag across the glass. Inside windows rarely need rinsing, they need degreasing and careful, patient buffing.
The Squeegee Advantage
Ask any professional window cleaner what separates their results from a DIY effort and the answer is almost always the same: the squeegee.
A good squeegee with a fresh, undamaged rubber blade removes solution from the glass in a single, controlled stroke. No second pass dragging residue back over clean glass. No cloth depositing fibres. Just clean glass, consistently. It takes a little practice to get right, but once you’ve got the technique, it’s genuinely satisfying.
The key points:
- Overlap each stroke slightly to avoid leaving a line of residue between passes
- Wipe the blade after every stroke with a clean, dry cloth – every single time
- Work top to bottom so you’re not pulling clean water over sections that have already started to dry
- Keep the rubber blade in good condition – a nicked or worn blade leaves lines every time, no matter how good your technique is
A decent squeegee costs between £10 and £25. Combined with a microfibre cloth and a bucket of clean water with a drop of washing-up liquid, it’s a setup that will beat most spray-based methods and it costs less than a branded cleaning kit from the supermarket.
When DIY Isn’t the Answer
Some window streaking problems go beyond technique and product choice. If your glass has deep mineral etching, scratches, or failed coating from a previous product, careful cleaning won’t produce a clear finish. The damage is in the glass itself, and no amount of wiping will fix it.
Similarly, if your double-glazed units have failed seals, you may be seeing condensation forming between the panes, something that looks like streaking from certain angles but genuinely cannot be cleaned away from either side. That’s a job for a glazier, not a microfibre cloth.
A good window cleaner will tell you honestly which category you’re dealing with. Most are happy to have that conversation.
The Pattern Worth Breaking
Streaky windows aren’t inevitable. They’re the result of specific choices, wrong products, dirty cloths, bad timing, hard water, quietly stacking on top of each other until the whole thing feels hopeless.
Change one of those variables and you’ll notice an improvement. Change all of them and you might finally have the clear, bright windows you’ve been chasing every time the sun comes out and ruins your morning.
