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Challenges & Pitfalls of RO

We live on a blue planet. But when it comes to freshwater — only a tiny fraction of all water on earth is readily accessible. Rivers and lakes which provide the water we use every day account for only 1/150th of one percent of the world’s total water supply.

This scarcity becomes even more apparent when we consider that over 96 percent of the Earth’s water is saline, and much of the remaining freshwater is locked away in glaciers and underground.

Desalination, the process of purifying seawater or brackish water, has emerged as one of the fastest growing means of technology to tap into the 96%, securing freshwater for current and future needs.

The overwhelming majority of desalination processes occur with the help of membranes through a technology called reverse osmosis (RO). Unfortunately, these solutions have a major impact on our planet.

What is RO exactly?

Reverse osmosis (RO) is a water purification technique that uses a semi-permeable membrane to remove ions, unwanted molecules, and larger particles from drinking water. In the process of desalination, reverse osmosis can effectively remove salt and other impurities from seawater, converting it into freshwater. The technique operates by applying pressure to the saltwater side of the membrane. This pressure overcomes the natural osmotic pressure, causing water to flow from the concentrated (salty) side to the dilute (freshwater) side, leaving the dissolved salts and other impurities behind. The result is pure, potable water that is safe for human consumption and agricultural use.

Reverse osmosis process. iStock/ttsz

While reverse osmosis has been proven to be a reliable solution, this technology comes with a wide range of challenges and pitfalls, and we must confront a reality: RO technology is simply unsustainable.

Here’s why keeping up RO simply is not feasible, if we want to preserve our blue planet for future generations:

A Sea of Chemicals

RO systems are synonymous with extensive chemical use. Cleaners, detergents, scale inhibitors, antiscalants, corrosion inhibitors, biocides, antifoulants, de-chlorinators, flocculants — the list goes on. Throughout the RO process, these chemicals are necessary for the maintenance and the pre- and post — treatment of input water. These chemicals can be harmful to the environment if they are not properly managed and disposed of.

Toxic Brine

Toxic brine has begun to leave its mark on our oceans. Brine is the highly concentrated, salt-rich water that is produced as a by-product of desalination. For every liter of freshwater produced, RO desalination generates approximately 1.5 liters of brine, which is typically discharged back into the sea. This salty brine has negative impacts on the marine environment: The high salt content causes changes in the water chemistry and harms aquatic life, including fish, crustaceans, and other marine organisms. The brine can also create “dead zones” in the ocean, where the increased salinity makes it difficult for other species to survive. In the Arabian Gulf, home to numerous desalination plants, increased salinity has led to a noticeable decline in the diversity and abundance of marine life. Additionally, brine often contains trace amounts of the chemicals used in the desalination process named above, adding an extra layer of pollutants.

The United Nations estimates that globally, desalination plants discharge 142 million cubic meters of brine daily — enough to cover the state of Florida under a foot of brine each year!

Brine discharge pipe and vent from a desalination plant. PHOTOSTOCK-ISRAEL / SCIENCE PHOTO LIBRARY

Energy and Cost

RO’s energy requirements pose another challenge, and these needs are not met by renewable sources making RO reliant on polluting and expensive fossil fuels. Even when PV panels are coupled to these systems, RO is not optimized for renewable energy meaning that voltage dips from variable renewable sources can damage the membranes and reduce output quality.

These energy requirements are also what makes it so expensive: 55% of an RO plant’s lifetime cost consists of energy. The levelized cost of water from RO systems also tends to increase over their lifetime. High maintenance requirements, degrading membranes, dependence on supply chains, and fluctuating energy costs contribute to an unpredictable and often rising cost structure. The Victoria Desalination Plant in Australia, for instance, faced escalating costs due to high energy prices and a series of plant shutdowns for membrane replacements, affecting water bills for end consumers.

Handling Fluctuating Water Quality

Lastly, one of the lesser-known constraints of RO technology is its inability to handle fluctuations in water quality or water quality that changes over time. In our changing climate, with increasing instances of saline intrusion, flooding, and other climate shocks, this limitation of RO could leave communities vulnerable at times when clean water is most critical. Take the recent floods in Pakistan, where salinity intrusion into freshwater sources spiked. An RO system would struggle to cope with such drastic changes, potentially leaving thousands without safe drinking water.

The sea of challenges surrounding RO paints a stark picture — we need a new wave of innovation in desalination. As we navigate towards a future where we aim to protect our oceans while securing drinking water, it’s clear we must move beyond RO to more sustainable, flexible, and cost-effective solutions. It’s time for a new standard in sustainable desalination — the future of our oceans, and our communities, depends on it.

Stay tuned for part two — where we will dive into transformative, sustainable alternatives to water provisioning.