There's not that much fresh water on the surface of the Earth.
Water is distributed across roughly 71% of the surface area of our planet, but the bulk of that water is essentially saline or salt water with some 34 grams of salts in a single kilogram. Saline groundwater and water from salty lakes comprises 97% of the water on Earth.
Most of the fresh water on the planet is trapped in ice sheets, ice caps, glaciers and icebergs, but a portion is also held in ponds, lakes, rivers and underground as groundwater in aquifers.
Even less of what's called "sweet water" is considered potable, or suitable for drinking without purification. The use of chemicals in agriculture, industrial and domestic processes has created a growing demand for the sort of analytical tools needed to monitor water quality.
Now a team of research scientists in the UK have created a device for developing countries which they say will make it easier to determine if drinking water is actually safe.
The team at the Department of Chemical Engineering and Bristol Robotics Laboratory at the University of Bath developed the sensor, said to be safe for use in rivers and lakes, and it's capable of real-time and continuous monitoring of water quality which was designed and output using 3D printing.
A fuel cell packed with bacteria produces a small but measurable electrical charge which, when the sensor detects contaminated water, can provide an alert that water is unsafe for drinking.
Laboratory trials have shown that the sensor can detect pollutants like cadmium. That's a significant result as it is a toxic by-product most often created by processes used in the electronics industry. Known to result in human health problems, those exposed to cadmium can develop a variety of cancers.
According to Dr. Mirella Di Lorenzo, a lecturer in Chemical Engineering at Bath, this new biosensor may be simple, but it can provide a critical warning which she likens to a sort of "canary in a coal mine" effect.
"Because this system uses live bacteria, it acts a bit like a canary in a mine, showing how these chemicals affect living organisms," says Di Lorenzo.
In this study, a small-scale single chamber air-cathode microbial fuel cell (SCMFC) fabricated by 3D printing was tested as a biosensor for continuous water quality monitoring.
Di Lorenzo says the device can rapidly detect the presence of cadmium in water with very high sensitivity and a low detection limit.
"This means we're able to monitor the level of pollutants in the water in real time without having to collect multiple samples and take them to a laboratory," she added.
It's thought that this new system might one day replace the current method used by researchers which analyzes the effects of water pollution by determining ways polluted water effects fish or plankton. It might also reduce the dependence researchers now have on mass spectrometry to measure water pollution. Using mass spectrometers is expensive and as they are delicate instruments, maintaining and operating them require experts. Di Lorenzo says that this latest device is cheap and accurate, and it's those factors which will prove a boon to users in developing countries.
Should you want to read the findings of the University of Bath team, you can check it out here.