VidyuthLabs
Water
Testing drinking water for lead, cadmium, arsenic and mercury: limits and on-site methods
Heavy metals in drinking water have no taste, smell or colour. The only way to know they are there is to test. Here is what the limits are, how laboratories measure them, and how portable electrochemical sensors make it possible to screen water on site.
Why heavy metals matter
Lead, cadmium, arsenic and mercury are toxic even at very low concentrations and they accumulate in the body over time. Lead affects the nervous system and is especially harmful to children. Arsenic in groundwater is a long-standing public-health problem in parts of India and South Asia. Cadmium damages the kidneys, and mercury the nervous system. Sources include natural geology, industrial discharge, mining, old plumbing and solder, and contaminated agricultural run-off.
The limits
In India, drinking-water quality is set by the Bureau of Indian Standards in IS 10500:2012. The World Health Organization publishes guideline values used by many countries. For these metals the numbers are:
| Metal | BIS IS 10500 (acceptable limit) | WHO guideline value |
|---|---|---|
| Lead (Pb) | 0.01 mg/L (10 µg/L) | 10 µg/L |
| Arsenic (As) | 0.01 mg/L (10 µg/L) | 10 µg/L |
| Cadmium (Cd) | 0.003 mg/L (3 µg/L) | 3 µg/L |
| Mercury (Hg) | 0.001 mg/L (1 µg/L) | 6 µg/L (inorganic) |
1 µg/L is one part per billion (ppb). These are tiny concentrations, so any useful test has to be sensitive at the low-ppb level.
How laboratories test
Reference methods include inductively coupled plasma mass spectrometry (ICP-MS), ICP optical emission spectrometry and atomic absorption spectroscopy (AAS). They are accurate and can measure many elements at once, but they need a laboratory, trained staff, gases and sample transport. Results usually take days, and the cost per sample limits how often water is tested.
Colour-change field kits exist for some metals, especially arsenic. They are cheap and simple, but they are mostly qualitative or semi-quantitative and can struggle near the limit values.
How electrochemical sensors test on site
The established electrochemical method for trace metals is anodic stripping voltammetry (ASV):
- Deposit. A negative potential is applied for a set time, reducing metal ions in the sample and plating them onto the electrode. This step concentrates the metals at the surface.
- Strip. The potential is scanned in the positive direction. Each metal oxidises and leaves the electrode at its own characteristic potential, producing a current peak.
- Quantify. Peak position identifies the metal, and peak height or area relates to its concentration, using calibration or standard addition.
Because the deposition step pre-concentrates the sample, ASV can reach the low-ppb range that drinking-water limits require. Lead and cadmium are classic ASV targets. Arsenic and mercury are usually measured on gold electrode surfaces, which is one reason electrode material and coating matter so much.
Why screen-printed electrodes make this practical
Older ASV used hanging mercury drop electrodes, which are toxic and unsuitable for the field. Modern methods use disposable screen-printed electrodes made from carbon or gold, often modified with nanomaterials or metal films such as bismuth to improve sensitivity and selectivity. Each test starts on a fresh surface, with no cleaning, polishing or mercury.
What a good on-site test looks like
- Sensitivity at or below the regulatory limit for the metal you care about.
- A sample preparation step simple enough to do in the field, such as adding a buffer.
- A clear pass or fail against the limit, with the raw data kept for records.
- Confirmation of positive results by an accredited laboratory when decisions depend on them.
On-site electrochemical screening does not replace accredited laboratory testing. It makes testing frequent and fast enough to catch problems early, and sends only the samples that matter to the lab.
How VidyuthLabs approaches it
Our AnalyteX handheld potentiostat runs voltammetric methods on NanoX screen-printed electrodes, each coated with nanomaterials for a specific test, including sensors aimed at lead, cadmium, mercury and arsenic. Results show on the device and sync to a mobile app. We are developing these applications in collaboration with BITS Pilani, Hyderabad Campus.
Need to test water for heavy metals? Tell us which metals and what kind of water, and we will tell you which sensor fits.