Start from the decision, not the sensor
It's tempting to buy a multi-parameter probe and measure everything. But every online sensor is a thing to calibrate, clean and maintain — and a reading nobody acts on is just cost. The right approach is the same as all good monitoring: decide what question you're answering (Is this water safe to drink? Is my discharge compliant? Is my treatment process healthy?), then measure the parameters that answer it. Here's what the common ones actually tell you.
The core parameters
- pH — how acidic or alkaline the water is. Drives corrosion, disinfection effectiveness and process chemistry; a licence limit for most discharges.
- Turbidity — cloudiness from suspended particles. A key potable-water safety and treatment indicator, and a discharge parameter; a turbidity spike often flags a process problem upstream.
- Conductivity / TDS — the level of dissolved salts. Indicates salinity, contamination or ingress, and matters for process water and irrigation suitability.
- Dissolved oxygen (DO) — oxygen available in the water. The heartbeat of biological wastewater treatment (too low and treatment fails) and a measure of river health.
- COD (chemical oxygen demand) — the organic pollutant load. A central effluent-compliance and treatment-performance parameter.
- Residual chlorine — disinfectant left in potable water. Confirms the water stays safe through the network; too little risks pathogens, too much causes taste and by-product issues.
- Temperature — cheap to measure and influential: it affects DO, reaction rates, disinfection and many sensor readings, so it's often measured alongside the rest.
Which to monitor, by water type
| Water | Usually most useful | Why |
|---|---|---|
| Potable / drinking | Turbidity, residual chlorine, pH, conductivity | Safety and disinfection through the network |
| Wastewater process | Dissolved oxygen, pH, flow, level | Keeping the biological process healthy |
| Final effluent / discharge | COD, pH, turbidity, conductivity (per licence) | Proving compliance with your water-use licence |
| Process / industrial | Conductivity, pH, temperature | Protecting equipment and product quality |
The catch: calibration and maintenance
Online water-quality sensors are only as trustworthy as their upkeep. Probes drift, foul and age — an uncalibrated pH or DO sensor can quietly mislead you, which is worse than no sensor. So a real programme budgets for calibration schedules, cleaning (especially in dirty water and wastewater), and sensor replacement, and ideally cross-checks against periodic lab samples. This is why "measure everything" backfires: each added parameter multiplies maintenance. Scope to what drives a decision, and the upkeep stays manageable.
Why pair sensors with a platform
A standalone probe with a local display tells one person, sometimes. The value comes when readings are continuous, trended, alarmed and recorded: a breach alerts the right person instantly, trends reveal slow drift before it's a problem, and the log becomes your compliance evidence. That's the job of the addaNet platform in our water quality & compliance work — turning sensor readings into alerts, trends and DWS-ready reports, with edge buffering so a load-shedding gap doesn't break the record. We help you choose the parameters that matter for your water and plan the calibration that keeps them honest.
This is general guidance; specific parameters, limits and methods should follow your water-use licence, the relevant SANS/DWS standards and your appointed advisers.
Frequently asked questions
Which water quality parameters should we monitor?
Only the ones that answer your question or meet a licence obligation. For drinking water, turbidity, residual chlorine and pH; for wastewater process, dissolved oxygen and pH; for discharge, COD, pH and turbidity per your licence; for industrial process, conductivity, pH and temperature. Scope to decisions, not to a probe's full parameter list.
What does each common sensor tell me?
pH shows acidity/alkalinity; turbidity shows clarity and suspended solids; conductivity/TDS shows dissolved salts; dissolved oxygen shows the health of biological treatment; COD shows organic pollutant load; residual chlorine confirms disinfection; and temperature affects most of the others, so it's usually measured alongside.
Do online sensors replace laboratory sampling?
No — they complement it. Online sensors give continuous trends and instant breach alerts between lab samples, while accredited lab analysis remains the reference for compliance and for parameters that can't be measured reliably online. Best practice cross-checks online readings against periodic lab results.
How much maintenance do water quality sensors need?
More than people expect. Probes drift and foul, so they need scheduled calibration, cleaning (especially in wastewater) and periodic replacement. An uncalibrated sensor can mislead you, so maintenance is essential — which is another reason to monitor only the parameters you'll actually act on.
Why connect sensors to a platform instead of using local displays?
Because the value is in continuous trends, instant alerts and a defensible record — not a number on a panel someone occasionally reads. A platform alarms a breach to the right person, reveals slow drift early, and logs everything for compliance, with edge buffering so load shedding doesn't leave a gap.