The water coming out of the tap in this room has been treated, monitored, and reported on by people whose job that is. Almost nobody reads those reports. This task is you reading one, measuring a few of the same things yourself, and writing something a person who is not a chemist could actually use.
Two measurements sit at the centre of it: what you can determine at this bench, and what the published record says. Where those two agree is reassuring. Where they differ, the interesting question is which one to trust, and why.
The situation
Every municipality in Ontario that operates a drinking water system produces an annual water quality report, and it is public. Ontario’s Drinking Water Quality Standards set legally binding limits for a long list of substances. Health Canada publishes the Guidelines for Canadian Drinking Water Quality, which are recommendations developed with the provinces and territories. Environment and Climate Change Canada publishes on the state of water in the wider environment — what enters it, and from where.1
Your job has three parts: measure, compare, and advise.
You are writing for a specific audience. Name them on the first line. Some that work well:
- A household deciding whether to buy bottled water, a filter jug, or nothing at all.
- The school community, in a piece for a newsletter or a poster in the hallway.
- A student council deciding whether to fund refill stations.
- A younger class, which is the hardest audience and the most revealing to write for.
Part 1 — What you can measure here
School equipment cannot do what an accredited laboratory does. It can do several real things well, and being honest about which is which is part of the task.
| Quantity | How you would measure it here | How good is the number |
|---|---|---|
| pH | Meter, or narrow-range indicator paper | Meter: good. Paper: a range, not a value |
| Total hardness | Titration with a standard hardness kit | Quantitative if the titration is done carefully |
| Chloride | Titration, or a test strip | Titration is quantitative; strips are semi-quantitative |
| Total dissolved solids | Conductivity meter, or evaporate a measured volume and mass the residue | Both are indirect; conductivity is a proxy, not a direct measurement |
| Free chlorine | Colour-comparison test kit | Semi-quantitative, and it changes on standing |
| Nitrate | Test strip | Semi-quantitative at best |
Your design decisions, written down and checked before you start:
- Which quantities you will measure, and why those. Three done well beats six done badly, and a report is judged on the quality of its evidence rather than the length of its table.
- Where and how you sample. Standing water that has been in the pipes overnight is not the same sample as water run for two minutes. Decide which you want, say why, and be consistent.
- How many replicates, and what agreement you will accept between them.
- What your controls are. Distilled water run through the same test is the obvious one, and it tells you whether your method reports something when there is nothing there.
- The resolution of every method you use, recorded before your first reading. A test strip that reads in steps has a resolution equal to that step, and no amount of squinting improves it.
Sampling, test kits, and one absolute rule about mixing
- Never combine household cleaning products, and never combine any two substances that are not on your approved procedure. Chlorine bleach with an acid, or bleach with an ammonia-based cleaner, produces toxic gases. This is exactly the topic where somebody is tempted to “test what happens”, and the answer is a hospital visit. Nothing is combined that is not on the list I have approved.
- Nothing sampled is drunk from lab glassware. Not the tap water you just collected, not the sample after testing, not ever. Once water is in a beaker it is a sample, not a drink.
- Test kit reagents are chemicals. Follow the kit’s own instructions exactly, wear eye protection, and treat used reagent as waste. Some hardness and chlorine reagents are irritants.
- If your method involves a titration, everything in Titrating an Acid applies: never pipette by mouth, rinse the buret with the solution it will hold, fill it below eye level, and read the bottom of the meniscus at eye level.
- If you evaporate a sample to find dissolved solids, use gentle heat and stop before dryness. A basin taken to full dryness spits. Hot glass and hot ceramic look identical to cold, so tongs, always.
- Do not sample a natural water body for this task unless we have arranged it, and never taste, wade into, or drink from one.
- Eye protection throughout, hair back, waste to the labelled containers, nothing returned to a stock bottle, and every incident reported however small.
Full agreement: Safety in the Lab and Lab Safety and WHMIS.
Part 2 — The published record
Find the water quality report for the system that supplies this building, and find the current Ontario Drinking Water Quality Standards. Look up the substances you measured, and look up two or three you could not measure but that the report covers.
Look the numbers up. Do not take them from me, or from memory
This page deliberately contains no limits and no measured values, and that is not an oversight. Standards are revised, municipal results change year to year, and a number remembered from a classroom is worth nothing in a report that somebody might act on.
Go to the source, record what it says, cite where you found it, and note the date or reporting period of the document. A figure without a date is not traceable, and a report built on undated figures cannot be checked.
Never invent a figure, a study, or an organisation. If you cannot find something, write that you could not — it costs you nothing here and an untraceable number costs you a great deal. See What Counts as Evidence and Reading a Data Table.
Then widen the frame. Where do the substances in water come from? Agricultural run-off, road salt in winter, landfill leachate, industrial effluent, storm sewer overflow, corrosion products from the distribution pipes themselves and from the plumbing inside a building. Some of these accumulate: a substance that does not break down and is added every year behaves very differently from one that is flushed through in a season, and your report should say which kind you are discussing.
Part 3 — The advice, and its costs
This is where the task stops being a lab and becomes a judgement.
Your audience wants to know what to do. Bottled water, a filter jug, a plumbed filter, a refill station, or nothing at all — each has a cost in money, a cost in effort, and a cost to something outside the household. Some of what you should weigh:
- What a filter does and does not remove, and what it needs to keep working.
- What bottled water costs per litre against treated tap water, and what its container costs to make, move, and dispose of.
- Who has reliable treated water and who does not, which in this country is not evenly distributed and is worth saying plainly.
- What the municipal system already does, and whether a household measure duplicates it.
A recommendation with no cost named is not a recommendation. It is a preference with a paragraph around it.
What to hand in
A report of three to four pages, addressed to your named audience:
- What you measured, how, and what you found. A data table with units, replicates, controls, and the resolution of each method.
- How your results compare with the published record. Not a verdict — a comparison, with the difference between your figure and the published one discussed in terms of your method’s precision.
- Where the substances come from, and which of them accumulate.
- Your recommendation, with costs named.
- Limitations. What your measurements cannot establish, and why. This is the section I read most carefully.
A sources page, in the format in Writing About Chemistry, with at least three sources of the right kinds: the municipal water quality report, Ontario’s Drinking Water Quality Standards, Health Canada’s guidelines, or Environment and Climate Change Canada. Each entry dated.
How it will be judged
| What I am looking for | Level 3 sounds like | Level 4 sounds like |
|---|---|---|
| Measurement design | Sensible quantities, measured properly | Fewer quantities, chosen because they are the ones this bench can do well |
| Data | Complete, with units | Replicates and controls included, and each method’s resolution stated |
| Comparison | Compares your values with published ones | Discusses whether a difference is larger than your precision, and what would settle it |
| Sources | Real, appropriate, cited | The right source for each claim, dated, with the guideline-versus-standard distinction used correctly |
| Pollutant origins | Names sources of contamination | Distinguishes what accumulates from what passes through, and says why it matters |
| The recommendation | Sensible, follows from the findings | Fits the audience, names the cost, and does not overclaim |
| Limitations | Names a limitation | Names what the method cannot detect at all, and says so before the recommendation rather than after |
| Writing | Clear and organised | The named audience could act on it without a chemistry course |
What sinks an otherwise good report
- A number with no source or no date. The whole task is about traceable evidence, and one untraceable figure puts every other figure in question.
- Treating a test strip result as a measurement. A strip that reads in steps gives you a range. Report the range.
- “The water is safe.” You measured three things with school equipment. Say what you measured, what it compared with, and what you did not measure — which is nearly everything on the standards list, including the substances that are hardest to detect and matter most.
- Confusing a guideline with a standard, or quoting one as though it were the other.
- A recommendation to buy something, with no cost and no alternative considered.
- Inventing a figure to fill a gap. The one thing that cannot be repaired by a rewrite.
Related discussion: The Air We Share takes the same question — a shared resource, cumulative effects, and who bears them — into the atmosphere.
Curriculum connection
E1.1
analyse the origins and cumulative effects of pollutants that enter our water systems (e.g., landfill leachates, agricultural run-off, industrial effluents, chemical spills), and explain how these pollutants affect water quality [AI, C]
Link to original
E1.2
analyse economic, social, and environmental issues related to the distribution, purification, or use of drinking water (e.g., the impact on the environment of the use of bottled water) [AI, C]
Link to original
E2.8
conduct an investigation to determine the concentrations of pollutants in their local treated drinking water, and compare the results to commonly used guidelines and standards (e.g., provincial and federal standards) [PR, AI]
Link to original
Footnotes
-
The words are not interchangeable and the difference matters for how you write your report. A guideline is a recommended value developed on health grounds; a standard is a limit written into regulation, which an operator is legally required to meet and to report against. A report that says “this exceeds the guideline” and a report that says “this exceeds the standard” are making different claims about what happens next, and using the wrong word is the kind of error a reader who works in the field will notice immediately. ↩