Inside a Pro’s Bucket: The Water, Additives, and Science of Window Cleaning

Written by pureseal123 on November 14, 2025. Posted in Blog, Pressure Washing

What Do Professional Window Cleaners Use in Their Water?

A 2000-word expert guide

Professional window cleaning may look simple from the outside — a bucket, an applicator, and a squeegee — but the water used in the process is far from ordinary. The chemistry, filtration, and additives used by pros have a dramatic impact on the finish, the speed of cleaning, and the longevity of results. Whether windows are cleaned by traditional hand-squeegeeing or with modern water-fed pole systems, the water itself plays a central role in ensuring spotless, streak-free glass.

This guide explains what professionals put in their water, why they use it, and how different cleaning methods influence water composition. You’ll also find tables, comparisons, cost considerations, and explanations of the science behind pure water.

1. The Foundation: Pure Water and Why It Matters

The most common and important substance professional window cleaners rely on is pure water. In this context, “pure” doesn’t simply mean clean tap water — it refers to water that has been purified to remove minerals, metals, organic matter, chemicals, and dissolved solids.

1.1 Why Normal Tap Water Causes Problems

Tap water contains minerals such as calcium, magnesium, sodium, iron, and silica. When water evaporates after cleaning, these minerals are left behind as spots or streaks. Even tiny amounts are visible on glass.

Average UK tap water contains 100–350 ppm (parts per million) of dissolved solids. Anything above 10 ppm is enough to leave visible residue on glass.

1.2 The Science Behind Pure Water Cleaning

Pure water has a natural property:
It is “hungry” for minerals and dirt.

Once minerals and impurities are removed, the water becomes a powerful natural solvent. It attracts:

• Dust

• Organic grime

• Bird mess

• Traffic film

• Pollen

• Airborne pollutants

This allows professionals to clean with no detergents at all when using a water-fed pole system.

1.3 Cost Consideration (Purification vs. Tap Water)

Even though pure water costs more to produce, it saves labour time because windows can be left to dry naturally without polishing.

2. Purification Systems and What They Put Into (and Remove From) Water

Professional cleaners do not add dirt-removing chemicals to pure water; instead, they process the water to remove impurities before use.

Here’s what they use:

2.1 Reverse Osmosis (RO) Units

RO systems push water through a semipermeable membrane, filtering out:

• Minerals

• Metals

• Particles

• Chlorine by-products

• Silicates

• Nitrates

This typically brings water from 150–350 ppm down to 5–20 ppm.

Professionals may use:

• Pre-filters (carbon and sediment filters)

• RO membrane

• Storage tanks

RO is economical for high-volume use.

2.2 Deionisation (DI) Resin

Deionisation removes the remaining dissolved solids after RO or can be used as a stand-alone purification method for low-TDS areas.

DI resin exchanges charged ions:

• Calcium → Hydrogen

• Magnesium → Hydrogen

• Sodium → Hydrogen

When used alone, DI can bring water from 150 ppm down to 0 ppm, but the resin exhausts quickly.

Cost Table: DI Resin vs. RO/DI Combo

2.3 Mixed Bed Resin

Most pros use mixed bed resin containing:

• Cation resin

• Anion resin

This ensures final polishing of the water to 0 ppm.

2.4 Final Rinse Water: 0 ppm

A digital TDS meter confirms that the processed water is completely pure.
A reading of 0–5 ppm is considered acceptable for professional use.

3. Additives Used in Traditional Bucket & Squeegee Cleaning

Unlike pure-water systems, traditional hand cleaning does require additives. These are designed to:

• Break down oil and grime

• Lubricate the squeegee

• Reduce drag

• Prevent streaking

• Improve cleaning speed

Below are the most commonly used additives.

4. Cleaning Detergents: What Professionals Add to Their Water

4.1 Professional Glass Detergent Concentrate

These detergents are formulated for:

• Minimising streaks

• Providing glide

• Emulsifying oily dirt

• Working with cold water

They often contain:

• Surfactants

• Wetting agents

• pH-balanced cleaning compounds

Typical Mix Ratio

4.2 Washing-up Liquid (Used Occasionally)

While professionals prefer purpose-made detergents, some still use washing-up liquid.

Why?

• Cheap

• Readily available

• Creates good glide

Why not ideal?

• Can leave residue

• Attracts dirt faster

• More streaking risks

4.3 Isopropyl Alcohol (IPA)

IPA is added for:

• Faster drying

• Improved cleaning in cold weather

• Eliminating greasy fingerprints

• Preventing freezing in winter

Typical ratio: 10–50 ml IPA per 10 litres of water

Cost:
A 1-litre bottle of 99% IPA costs around £5–£10, so a 50 ml addition costs about £0.25–£0.50.

4.4 Ammonia-Based Additives

Less common today but still used for:

• Removing nicotine film

• Cutting heavy grease

• Cleaning commercial storefronts

Ammonia must be used carefully and diluted at 1–2 teaspoons per bucket.

4.5 Vinegar (Acetic Acid)

Some professionals use small amounts to break down:

• Water spots

• Mineral deposits

• Soap scum

Typical mix: 50–100 ml distilled vinegar per 10 litres

4.6 Flow Enhancers / Wetting Agents

These additives allow water to sheet evenly across glass, preventing droplets and streaks.

Wetting agents are common in:

• High-speed commercial cleaning

• Hydrophobic glass surfaces

5. Additives for Specific Situations

5.1 Hard-Water Spot Removal

Professionals may use:

• Mild acidic additives (citrus-based or buffered acids)

• Mineral-dissolving solutions

These are only added for restoration work, not routine cleaning.

5.2 Cold-Weather Additives

To prevent freezing and help water evaporate:

5.3 Anti-Static Agents

Used on interior glass where dust settles quickly.
These additives reduce dust attraction after the window dries.

6. Why Some Professionals Prefer Pure Water Without Any Chemicals

6.1 Chemical-Free Cleaning

Pure water fanatics argue:

• No residue left on glass

• No environmental impact

• No need for squeegeeing

• No ladder use when paired with a water-fed pole

• Safer and faster

6.2 Long-Term Effects on Glass

Using detergents can leave a microscopic film that:

• Attracts dirt quicker

• Requires more frequent cleaning

Pure water avoids these issues.

7. Water-Fed Pole (WFP) Cleaning: What Goes in the Water?

Short answer: Nothing but pure water.

Why no detergents?

• They leave residue

• They disrupt the sheeting action

• They would require rinsing

• They reduce the natural cleaning ability of pure water

The WFP method relies entirely on the natural solvent behaviour of mineral-free water.

8. Comparison: Traditional Cleaning Water vs. Pure Water Systems

9. Example Water Recipes Professionals Actually Use

9.1 Traditional Cleaning (General Windows)

• 10 L of tap water

• 10 ml professional glass detergent

• Optional: 20 ml IPA for quicker drying

Total cost: Approx £0.25–£0.40 per bucket

9.2 Traditional Cleaning (Greasy Shopfronts)

• 10 L water

• 10–20 ml glass detergent

• 5 ml ammonia or citrus additive

• Optional: 30 ml IPA

Total cost: £0.35–£0.60 per bucket

9.3 Pure Water WFP Cleaning

• 100% purified RO/DI water (0 ppm)

• No detergents

• No chemicals

• No additives

Cost varies: £0.01–£0.05 per litre produced

10. Equipment That Influences Water Composition

Not an additive, but equipment plays a key role in water quality.

10.1 Sediment Filters

Remove dirt, sand, and rust.

10.2 Carbon Filters

Remove:

• Chlorine

• VOCs

• Organic matter

10.3 RO Membranes

Remove 90–99% of dissolved solids.

10.4 DI Resin

Polishes water to 0 ppm.

10.5 Pumps and Controllers

Ensure correct flow and pressure.

11. How Window Cleaners Test Their Water

Professionals use:

• TDS meters

• Inline water monitors

• Colour-changing DI resin indicators

A reading above 10 ppm tells them it’s time to change resin or filters.

12. Environmental Impact: Do Additives Matter?

Pure water:

• Leaves no chemicals

• Requires no detergent

• Reduces runoff pollution

Traditional detergents:

• Biodegradable formulas are common

• Residue quickly breaks down outdoors

13. Safety Considerations

Most additives are mild, but there are precautions:

• IPA is flammable

• Ammonia must not be mixed with bleach

• Acidic cleaners must be diluted

• Cleaning solutions should never be stored in food containers

14. The Future: Nano-Enhanced Water and Innovations

Emerging technologies include:

• Electrolysed water

• Ozone-infused water

• Nano-bubble water

These aim to improve cleaning performance without chemicals.

Conclusion

Professional window cleaners use a wide variety of substances in their water depending on the cleaning method:

In Pure Water Systems —

They use nothing except purified water, processed through:

• Reverse osmosis

• Deionisation

• Mixed bed resin

• Carbon and sediment filtration

This water is 0 ppm, leaving glass perfectly spot-free when it dries.

In Traditional Hand Cleaning —

They add substances such as:

• Professional window cleaning detergents

• Isopropyl alcohol

• Ammonia (rarely)

• Vinegar

• Wetting agents

• Anti-freeze additives (in winter)

Each has a specific purpose: lubrication, degreasing, quick drying, or improving glide.

Both methods are effective, but the choice of additives — or the absence of them — depends entirely on the professional’s chosen system, environment, and the type of dirt being cleaned.

15. Temperature and Water Performance in Professional Cleaning

Water temperature plays a surprisingly large role in professional window cleaning. While pure water is typically used cold, traditional bucket cleaners may adjust temperature depending on weather and grime levels.

Cold Water (5–15°C)

• Ideal for pure-water systems

• Maintains DI resin longevity

• Reduces streaking risk

• Less evaporation, giving more working time

Warm Water (20–40°C)

• Cuts through grease more effectively

• Helps dissolve pollen and organic films

• Used in winter to prevent freezing on tools

Hot Water (50°C+)

• Only used with specialised systems

• Effective for heavy commercial grime

• Speeds up cleaning of frames and sills

Cost Impact

Heated pure-water systems may add £0.50–£2.00 per job in energy cost but greatly improve winter efficiency.

16. How Professionals Adjust Water for Different Types of Glass

Not all glass behaves the same. Coatings, hydrophobic layers, tints, and treatments all influence what goes into the cleaner’s water.

Untreated Standard Glass

• Works well with any professional detergent

• Pure water leaves perfect results

Hydrophobic Glass

• Repels water naturally

• Causes droplets instead of sheeting

• Professionals may add wetting agents to improve coverage

Self-Cleaning Glass (TiO₂ Coated)

• Requires pure water only

• Detergents can disrupt the coating

• Gentle scrubbing pads recommended

Tinted or Film-Coated Glass

• Needs pH-neutral solutions

• No abrasive chemicals

• Very diluted detergents preferred

By adjusting water composition, professionals avoid smearing, damage, and warranty issues.

17. Container Hygiene and How It Affects Water Quality

Even the cleanest chemical mix can fail if stored in contaminated containers. Professional window cleaners maintain strict hygiene for buckets, tanks, and hoses.

Common Contamination Issues

• Algae growth in tanks

• Bacteria in hose lines

• Residue from previous detergents

• Rust particles from fittings

Hygiene Routine

Poor container hygiene can raise TDS readings, meaning even purified water may leave streaks.

18. Additives Used for Commercial High-Traffic Windows

Retail stores, restaurants, and public buildings often have glass exposed to more difficult contaminants such as fingerprints, cooking vapours, air pollution, and vehicle exhaust.

Professionals may adjust their water to include:

Grease-Breaking Detergents

Designed to tackle:

• Traffic film

• Cooking oils

• Handprints from glass doors

Solvent Boosters

Added in tiny amounts (5–10 ml per bucket) to dissolve:

• Window vinyl adhesive residue

• Sticker marks

• Crayon or marker

pH-Adjusted Water

Slightly alkaline mixes break down oily film faster without damaging seals.

Despite these additives, the final rinse often uses pure water for a flawless finish.

19. The Role of Foam, Bubbles, and Glide in Water Mixtures

The “feel” of the water — how it behaves on the glass — is crucial for traditional cleaning. Pros often judge their mixture by the glide on the squeegee rather than just the cleaning power.

Foam Level

• Light foam is preferred

• Too much foam reduces visibility

• Too little foam reduces lubrication

Bubble Structure

Small, tight bubbles indicate:

• Proper dilution

• Good glide

• Ideal detergent performance

Glide

A well-made mixture allows:

• Fast squeegee strokes

• Less wrist strain

• Cleaner edges

• Fewer touch-ups

Professionals develop a personal “recipe,” often adjusting day-to-day based on humidity, temperature, and glass condition.

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