Our tour guide unlocked a solid metal door, and we descended into the depths of Lyon, France to find ourselves in a magnificent vaulted reservoir filled with glistening, clear water.
Most of us don’t consider the effort required to pump water up as we pour ourselves a glass at home. Yet obtaining water has been a considerable struggle all throughout human history, including at present.
Here we share a reflection on how nature has been solving this problem since the evolution of vascular plants during the middle Silurian period, approximately 443 to 419 million years ago.
Shockingly, potable water has only been readily available to the people of Lyon for the last half-century. Strategically located at the confluence of the Rhône and Saône rivers, Lyon was the Gallic capital during the Roman Empire. These rivers primarily served as means of transportation for merchandise, since the water was not clean enough for Roman fountains and baths. So, the Romans did as Romans do, and built aqueducts. For a time, fresh water was abundant. Yet, the fall of Rome saw the destruction of these aqueducts—the lead stolen and the stone reused—and gave rise to a prolonged period of water woes for the quickly growing city.
Wells were dug, alleviating some of the dire lack of potable water, but major disease outbreaks occurred with devastating regularity. In the mid-14th century, half of Lyon’s population died during the Black Death, a death toll worsened due to unsanitary conditions. Up until the 1850’s, the people of Lyon were still lining up at wells with buckets to haul water back to their homes. Despite its persistent water issues, Lyon continued to prosper with bustling trade fairs, leading authorities to finally decide to improve the water supply and distribution system.
In 1856, l'usine des eaux de Saint-Clair was constructed, with three large, vaulted, underground basins (~3,500 m2, a bit larger than an NBA basketball court) that naturally filtered water from the Rhône River. But it still needed to be pumped up to the surface and into homes, which required an enormous amount of force. This was accomplished with Cornish steam pumps aboveground, measuring 20 m high and 200 tons (as tall as a four- story building and weighing almost as much as the Statue of Liberty), that pumped ~20,000 m³ of water per day to the different Lyonnais arrondissements. This construction was a massive feat, completed in record time, but ended up providing only 1/4th of the water requirements and was very costly in coal combustion. In 1910, the steam pumps were replaced by electric pumps and then ultimately dismantled in 1934, only 78 years after the plant’s opening. Not the grandiose solution Napoleon III envisioned.
In 1966, the city started over with many proposed ideas, including piping water from one of the large Swiss lakes, Lake Geneva, some 115 km (96 mi) away. The Swiss were not keen on this. Today, the Lyonnais get their water through a combination of a large filtration field, 114 wells, and water treatment plants.
Lyon’s story is not unique. Every location humans inhabit requires access to potable water. But this is not a uniquely human experience. This is a shared struggle for most terrestrial life and other lifeforms, notably plants, have found a much more ingenious and much less laborious method to grab a drink.
The privileged individuals who have stood in a grove of coastal redwoods, Sequoia sempervirens, know their sheer, towering splendor and the frustration of being unable to fit a tree into a single photo, no matter how far you walk back. They might not have as much heft as their montane cousin, the giant sequoia, Sequoiadendron giganteum, but coastal redwoods are taller on average, reaching up to 116 m (380 ft) in height. But, returning to the subject of water, how do these towering behemoths quench the thirst of their prickly needles at the tippy top? These giants, most terrestrial plants, and even a few animals, like the thorny devil lizard, take advantage of the intermolecular attraction of water molecules—water molecules have separation anxiety—to enact what is called capillary action.
You might not have heard the term ‘capillary action’ before, but you have experienced it. Think of when you put a piece of paper towel in water and see the water climbing upwards in defiance of gravity. Some people make use of it to water their plants while away on vacation with wick watering, also known as capillary irrigation. But plants harness capillary action at a physiological level.
When water evaporates from tree leaf stomata, pore-like structures on the leaf surface, this creates a negative pressure within the leaf and a pulling force within the tree’s transportation tissue called the xylem. This ‘transpiration pull’ in tandem with capillary action—the cohesion of water molecules to each other and adhesion to the xylem walls—allows the water to climb upwards from the roots, through the xylem, and to the canopy. The tree acts essentially like a long straw where evaporation at the top creates a sucking action to bring the water up. This is, of course, a simplified description of the entire process, but you get the gist.
As we exited from the underground reservoirs into the cold, winter day, we had a new appreciation for the water flowing from our tap. Our pitiful, anthropogenic struggles to obtain water are in stark contrast with the magnificent redwoods’ ingenuity. They don’t need to lift a needle to quench their thirst. They let physics do the work for them.
If plants are so ingenious, why have people not thought to take advantage of the same processes?
The cohesion-tension theory dates back to the end of the 1800s, and our understanding of water transportation in vesicular plants has improved considerably since. However, these processes are fickle, very challenging to master, and were out of reach for human technologies for a long time. Recent advancements in material sciences have allowed people to apply capillary action and evaporation tension to improve desalination, helping alleviate freshwater water shortages. But on the whole, we are far from competently employing these forces. Nature remains leagues ahead.
