Onsite water testing by sales reps — what the demonstrations don't tell you

How the free water test works

The call usually comes from someone offering a complimentary "water quality assessment" for your home. There's no cost, no obligation, and it takes less than an hour. You agree. A representative arrives with a kit of equipment, asks for a glass of your tap water, and proceeds to run a series of tests that produce visually striking results — often brown or black sludge, cloudy water, or alarming colour changes that appear to show your tap water is contaminated.

By the end of the visit, you've been presented with a filter system that costs between $3,000 and $8,000, often with same-day or next-day urgency pricing. The demonstration appeared scientific and the results appeared genuine. The problem is that the most dramatic tests are not measuring what the representative claims they're measuring.

This article explains the science behind the three most common demonstration techniques, what they actually show, and what a legitimate water quality assessment looks like.

The electrolysis trick — the brown sludge that comes from the electrode, not your water

The most widespread demonstration involves a device with metal rods (electrodes) that are dipped into your tap water. An electrical current is applied. Within seconds, your water turns yellow-brown or produces dark sludge. The representative explains that this shows contamination, heavy metals, or dangerous particles in your supply. They then run the same test on their filtered water — which stays largely clear — to show you the difference their product makes.

This is one of the most well-documented sales demonstrations in consumer protection literature, and it is deliberately misleading. Here is what is actually happening:

The process is electrolysis — passing electrical current through water. When you do this, the iron electrode oxidises, producing ferric hydroxide, which is the rust-coloured sludge you see. The equation is: Fe → Fe³⁺ + 3e⁻, followed by Fe³⁺ + 3OH⁻ → Fe(OH)₃. The sludge comes entirely from the iron electrode dissolving into the water. It does not come from contaminants in your water supply.

The reason your tap water produces sludge and their filtered water does not is simple: tap water contains dissolved minerals (calcium, magnesium) that allow it to conduct electricity. Their filtered or pre-prepared water has had minerals removed, so electricity cannot flow, so no electrolysis occurs and no sludge forms. The test proves nothing about contamination — it proves only that your water contains minerals, which is normal and in most cases healthy.

The TDS meter — measuring minerals, not safety

A TDS (Total Dissolved Solids) meter is a simple device that measures the electrical conductivity of water and expresses the result in milligrams per litre. Conductivity increases as dissolved mineral content increases. The representative dips this meter into your tap water, reads out a number — perhaps 250, 400, or even 600 mg/L — and presents it as evidence of contamination.

The problem is that TDS measures all dissolved solids, the great majority of which in Australian mains water are harmless minerals: calcium, magnesium, sodium, potassium, bicarbonate. These minerals are not contaminants. In fact, the World Health Organisation recommends a TDS of 100–300 mg/L as optimal for drinking water taste and mineral content, and some studies suggest water with very low TDS (below 50 mg/L) may not be ideal for long-term consumption.

Perth tap water typically reads between 150–400 mg/L depending on the zone — numbers a sales representative will characterise as alarming but which are within normal ranges. Sydney and Melbourne water is softer and typically reads 50–150 mg/L. A TDS reading alone cannot distinguish between a glass of calcium-rich spring water and a glass of water containing actual contaminants.

What TDS cannot detect: bacteria, viruses, chlorine and its byproducts, PFAS compounds, pesticides, heavy metals at typical concentrations, or any organic chemicals. The most dangerous water quality issues are completely invisible to a TDS meter.

The chlorine colour change — the dye test that proves very little

A third common demonstration involves adding drops of a chemical reagent (typically OTO — orthotolidine — or a similar indicator) to your tap water, which produces a yellow colour proportional to the chlorine content. The representative then runs the same test on filtered water, which stays clear, to show chlorine has been removed.

Chlorine is indeed present in Australian mains water — Water Corporation and other state utilities add it deliberately to prevent bacterial growth during distribution. Its presence is not a sign of contamination; it is a sign that your water authority is doing its job correctly. The question is not whether chlorine is present but whether the concentration is within safe limits, which for Australian mains water it virtually always is.

The test also conflates chlorine (which can be tasted at higher concentrations) with chloramine (the more common form of disinfectant now used by most Australian utilities), and does nothing to identify other contaminants. Carbon block filtration is effective at reducing both chlorine and taste — but whether you need it depends on whether your local water has a detectable chlorine taste, not whether a colourimetric test turns yellow.

The psychological tactics that accompany the tests

Beyond the demonstrations themselves, in-home water filter sales typically use a structured set of psychological pressure techniques that consumer protection researchers have documented extensively. Understanding them helps you maintain clarity about the decision you're being asked to make.

• The both-person rule: Many representatives require both partners to be present for the demonstration. The stated reason is usually courtesy or efficiency. The actual reason is to prevent one person from objecting privately to the other — and to prevent either partner from stepping away to research the claims being made.
• The time anchor: Demonstrations are deliberately extended to 90 minutes or two hours. The longer you've been engaged, the greater the social cost of saying no at the end. This is a known principle of commitment and consistency in sales psychology.
• The fear-then-relief structure: The demonstration is designed to create anxiety (your water is dangerous) followed by relief (but we can fix it). Decisions made in a fear-then-relief state are less rational than decisions made calmly after independent research.
• Same-day pricing: Significant discounts that expire if you don't sign today are a classic high-pressure closing tactic. Legitimate products do not genuinely require same-day decisions.
• Referral incentives: Offers of free cartridges or cash for referring friends are designed to enlist you as a social proof mechanism before you've had time to reconsider the purchase.

What legitimate water testing actually looks like

If you genuinely want to understand your water quality — and in some circumstances, particularly for bore water or properties near contamination sites, this is worth doing — here is what a credible assessment involves.

For most Australians on mains water in a major city, Water Corporation and equivalent state utilities publish detailed annual quality reports for each supply zone. Your water authority's website is the most credible first source of information about what is actually in your water — and it's free.

If you want independent testing beyond what the utility publishes, NATA-accredited laboratories in all states accept domestic water samples. A comprehensive potable water panel costs approximately $120–$350 depending on the parameters tested, and will produce a written report referencing Australian Drinking Water Guidelines. This is qualitatively different from a sales demonstration in your kitchen.

Test Type	What it measures	What it misses	Usefulness for purchase decision
Electrolysis	Mineral content (via conductivity)	Everything relevant — bacteria, chemicals, PFAS, metals	None
TDS meter	Total dissolved solids (mainly minerals)	Bacteria, viruses, organic chemicals, PFAS	Limited
Chlorine strip	Free chlorine level	Chloramines, all other contaminants	Partial
NATA lab panel	30–80 specific parameters with measured values	Nothing material if panel is comprehensive	High
State utility report	Full compliance testing across all regulatory parameters	Property-specific issues (old pipes, tank)	High

What to do if a rep is in your home

You are under no obligation to watch the full demonstration, answer questions about your household, or hear out the pricing. You are allowed to end any sales visit at any time. Some practical approaches:

• If you're curious about the demonstration, ask the representative to add salt to their filtered water and redo the electrolysis test. Their response will be informative.
• Ask whether the representative is a licensed water quality assessor and whether they can provide NATA-accredited results. If not, their test is a sales tool, not a professional assessment.
• Take nothing they leave behind as scientifically authoritative. Request any claims in writing and give yourself at least a week to research independently before making a decision.
• If you did sign and want to cancel, check your rights under the Australian Consumer Law cooling-off provisions — typically 10 business days for unsolicited sales agreements.

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