Back in 1748, the French physicist Jean-Antoine Nollet carried out a deceptively simple experiment.

He took a bag made from a pig’s bladder, filled it with wine, and immersed the bag in water. After some time, the bag began to swell. Water was entering the bag through its walls, creating pressure without the use of any pump.

This experiment revealed a fundamental principle: if there is a semi-permeable membrane and a difference in the concentration of substances, water will naturally move from the low-concentration side to the high-concentration side on its own.

Almost a century later, in the 1820s, another French physiologist, Henri Dutrochet, introduced the term describing this universal process: osmosis. It is the key to understanding how cells and plants function. The word “osmosis” descends from the Greek word “ōsmós”, meaning “push” or “thrust.”

A Bucket of Flowers

You don’t need a lab to see osmosis at work – just look at a bucket of flowers. When water is available, it moves from outside the cells into the interior where the concentration of salts is higher. As internal pressure builds up, the leaves and flowers remain firm and bloom. When water is scarce, intracellular pressure drops and the plant wilts.

Turning the Idea Around: Reverse Osmosis (RO)

A standing or wilting flower is osmosis in action. At its core, osmosis can be described very simply: water moves toward the region with a higher concentration of dissolved substances.

The key question that followed was: if water naturally flows into a higher concentration solution – meaning fresh water naturally seeks to mix with salty water – can we force it to move in the opposite direction, thus reversing the process? The answer is yes, by applying pressure.

For a long time, however, this remained more of a scientific concept than a practical solution. The real breakthrough came in the mid-20th century with the development of synthetic polymer membranes. Without them, modern watermakers would not exist. A functional membrane blocks dissolved salts while allowing water molecules to pass through.

Moving Onboard

To become the modern watermakers we see onboard boats and yachts today, the system has undergone several fundamental breakthroughs.

The Clark Pump and Energy Recuperation

In a conventional water maker, a powerful pump pushes saltwater through a polymer membrane that blocks dissolved salts while letting fresh water through. The pump pressurizes and pushes about 10 liters of saltwater, but only 1 liter passes through to be cleared of salt. In a conventional system, the remaining 9 liters – the brine – are simply discarded overboard.

Seawater reverse osmosis typically requires pressures of around 55–70 bar, making it an inherently energy-intensive process.

The game changed in the early 1990s with an invention by Tom Clark. He realized that those 9 liters of brine carry a significant amount of energy used to pressurize them. The Clark Pump recovers this energy by cycling it back into the system. The brine, which was previously wasted, is directed into the Clark Pump to help create pressure for the incoming water. This moved the energy efficiency of these systems to an entirely new level, reducing energy consumption by up to 70–75% compared to conventional systems without energy recovery.

Spiral-Wound Membrane Elements

A membrane is one thing; a compact, scalable membrane module is another. Spiral-wound elements were a major practical breakthrough because they provided reverse osmosis systems with high packing density and a small footprint, which is crucial for marine installations.

Better Pretreatment and Fouling Control

A huge part of real-world progress has occurred outside the membrane itself: better filtration, cleaning and fouling management. Modern RO systems last longer and operate more reliably because of sophisticated pretreatment of saltwater and improved operational controls.

Sophisticated Control

Today, improvements in watermakers are concentrated on a new generation of membranes, the efficiency of electrical circuitry, computer controls and automation. The goal is to minimize maintenance and achieve deeper and smarter integration into onboard systems.