Currently, one in four people in the world drink water contaminated with faeces. What’s more, one in three lacks access to safe drinking water, resulting in 165 million cases of Dysentery each year – the equivalent of half the US population. If those of us in the UK find these figures shocking, it’s only because we have the good fortune of living in a land that provides water so clean that whenever we are thirsty, we just need to turn on the tap. Compare ourselves with the Ugandans and we can see how lucky we are: 51% of the country lacks access to safe water; the urban population spends as much as 22% of its income just to buy clean water from vendors.

Measuring Water Quality

Many different factors are considered when measuring water quality as it is essential we do not drink water that contains harmful chemicals or pathogens. Water can also be contaminated by human or chemical waste without proper disposal, especially in less developed countries, which leads to people falling ill. Lead poisoning affected the ancient Romans who failed to understand that their lead pipes caused health issues. In Victorian London, cholera ran rampant as there was no proper waste disposal at the time. Therefore, being the most convenient method, they would throw their waste out of the window and into the street; where the public water supplies got contaminated (and unfortunate members of the public received a nasty surprise). Although the worst may be in the past, the effects of poor water quality should not be understated as 15 million people are infected with typhoid every year, which is roughly equivalent to the size of Zimbabwe’s population. These figures show that we are still a long way from supplying safe drinking water worldwide, with less developed areas such as Africa and Southern Asia most affected.

So how could we measure the water to ensure that it is safe? Some common tests are to test the pH, conductivity, the dissolved oxygen and turbidity (suspended particles in water) which may reveal chemical contamination in the water. Biological tests are also carried out to identify harmful pathogens that may be present.

There are also sets of standards that are applied to regulate drinking water. When it comes to purifying water, more may not mean better. The WHO recommendation – that TDS (total dissolved solids) should be under 1000ppm (parts per million) for safe drinking – is a vague guideline at best. Government officials overseeing public health still have to decide what kind of balance to strike: anything above 600ppm should probably be filtered further, but sift below 250ppm and they risk depriving their citizens of some of the minerals needed to maintain optimal health. There are many different values that can be obtained as there are particles of many different sizes in the water.

Reverse Osmosis

To explain Reverse Osmosis, it is useful to first understand the process of Osmosis. Osmosis is the net movement of solvent molecules across a semipermeable membrane from areas of higher water potential to lower water potential. A common example of the process is the absorption of water by plant roots. If you haven’t already guessed that Reverse Osmosis is the exact reverse of osmosis, it’s exactly what is says on the tin.

Osmosis is the scientific principle underlying desalination and pathogen removal, and conversely Reverse Osmosis is induced by applying pressure on the side of a mass that has lower water potential, so that the solvents there will penetrate the semipermeable membrane and enter into the region with higher water potential. Or simply put, you can get cleaner water if you push dirty water through the membrane.

Effectiveness and Efficiency

However, how effective is this method? Around 90-99% of contaminants are removed, making this an extremely effective filtering method. The technology is well known for being able to remove a broad range of contaminants.

The systems nowadays are so compact that they can even be portable, so they can conveniently fit in your water jug. The regular systems are generally quite slow at filtering water at a painstakingly slow rate of only around 60-90 ml per minute. Though faster systems can filter 1 litre of water per minute, which can fill a regular glass of water in 12 seconds, still slow but not unreasonable. With multiple units, the process can actually be very quick though the cost would also be high, reaching £50,000 for one good industrial unit. The current systems are not very efficient either as the best systems waste around 4 litres of water to produce 1 litre of clean water, this means that it is only a 20% efficiency in volume of water filtered, which is quite a low figure compared to other filters. However, there is a new emerging technology that is capable of turning the volume of waste water to 0; coined “ZeroWaste”, it uses another system to circulate the water, removing all water waste. The future is still looking bright as we continue to innovate and optimise this technology as there is still much room to improve.