Throughout history, clean and potable water has been one of the most prized possessions, without which no human civilization could have ever sustained itself. Not only is water crucial for drinking and food preparation, but also for agriculture, cleaning and the production of countless materials, chemicals and much more. And this isn’t a modern problem: good water supplies and the most successful ancient cultures go hand in hand.

For instance, the retention and management of fresh water in reservoirs played a major role in the Khmer Empire, with many of its reservoirs (baray) surviving to today. Similarly, the Anuradhapure Kingdom in Ceylon (now Sri Lanka) featured massive reservoirs like Kala Wewa that was constructed in 460 CE with a capacity of 123 million m³. In the New World, the Maya civilization similarly created reservoirs with intricate canals to capture rainwater before the dry season started, as due to the karst landscape wells were not possible.

Keeping this water fresh and free from contaminants and pollution was a major problem for especially the Maya, with a recent perspective by Lisa J. Lucera in PNAS Anthropology suggesting that they used an approach similar to modern day constructed wetlands to keep disease and illness at bay, while earlier discoveries also suggest the use of filtration including the use of zeolite.

Resource Management

In climates where rainfall is plentiful, and where wells can fill in gaps, extensive water management is not a major concern. This is where the civilizations of Mesoamerica provide good illustrations of the effects this can have on societies, with the Aztec and Inca using aqueducts to bring mountain spring water to their cities, while the Maya in their region with a karst topography had to capture every drop of rainwater before it would vanish within the hollowed-out structures that are a distinctive feature of these soluble carbonate rock landscapes.

This meant that the only time when the Maya could refill their reservoirs was when it rained, which also placed significant restrictions on how much water would be available to any population. It is postulated that it was a drought and reservoir pollution led to the eventual abandonment of the Mayan city of Tikal (ti ak’al in Yucatac Maya, but Yax Mutal (‘First Mutal’) according to inscriptions within the city) after the Late Classic Period (~900 CE). This preceded the Terminal Classic period, during which much of the lowlands were abandoned.

There is strong paleoclimatological evidence for a sustained drought between 800 – 1000 CE (likely related to the Medieval Warm Period) in and around the Yucatán Peninsula, coinciding when archeological evidence shows a reduced human presence in these lowlands by the Maya. It’s thought that these droughts coincided with epidemic diseases in combination with dense populations and intensification of agriculture with associated ecological destruction. The post-classical Maya period featured far less dense cities, and despite the often used term of ‘Classic Maya Collapse’, Mayan society was only regionally affected and persists to this day, despite efforts by European invaders and associated occupation over the centuries.

Filtration

Water filtration is something that happens not just with man-made structures and mechanisms, as anyone who uses water from springs and wells knows. The granular structure of soil serves to filter out larger and smaller contaminants as well as bacteria and other potential disease carriers. This same principle can be applied with artificial water filtration systems, with the Corriental water reservoir at the city of Tikal providing evidence that the Mayans even used the zeolite mineral for its water purification properties.

This was discovered by Kenneth Barnett Tankersley and colleagues, and published in 2020 in the journal Scientific Reports. They discovered that the water in this reservoir was filtered through a mixture of zeolite and coarse crystalline quartz. Zeolite is interesting, as it has adsorbent and ion-exchange properties which make it a popular choice even today for water purification to the point where most zeolite is synthesized for this and other purposes.

As for whether this extensive filtration in Mayan reservoirs was common is unknown, as the authors succinctly point out that the number of excavations of these reservoirs is quite limited. The presence of zeolite would have significantly helped with filtering out contamination from microbial sources like cyanobacteria and toxins such as cinnabar (mercury(II) sulfide). The latter is both a historically common brilliant red pigment as well as a good source of toxic mercury due to its mercury sulfide composition. Unfortunately this kind of filter does not help against mercury from volcanic sources due to its very small particle size, meaning that this type of contamination would have built up over the years in reservoirs.

Circle Of Life

The term ‘constructed wetland‘ pretty much gives away the concept: these create an artificial wetland ecosystem where plant and often also animal life work to treat sewage, greywater, stormwater runoff, and wastewater in general. They provide both a filtration function and a remediation one, with the vegetation along with microbial life serving to break down and process excess elements, while maintaining a healthy pH and nutrient levels.

In the mostly stagnant water reservoirs which the Maya maintained, preventing the build-up of organisms and harmful pollutants was essential, leading to likely extensive use of aquatic plants in these reservoirs. This is reflected in the headdresses, architecture and other elements of Mayan culture where the clean water-loving water lily (nymphaea ampla) is prominently displayed and associated with prosperity and the leadership.

Likely many different aquatic plants were used in combination with water lilies, along with various types of fish. This would have helped to deal with pests like mosquitoes and their aquatic offspring, reduce evaporation and creating a self-sustaining cycle where the waste from the fish would have provided nutrients for the plants, who themselves would have provided shade and food for these fish. Settlement maps show that the Maya did not generally build residences near the reservoirs, likely keeping human waste run-off to a minimum.

This healthy system did however begin to break down during the Late and Terminal Classic period, with the sediment record showing a gradual increase in contamination from cyanobacteria and human waste. This gives a sobering insight into the final years of the city of Tikal and areas like it that got hit worst by the drought.

Lessons For Today

Although we often like to regard droughts and access to potable water as historical problems, even today one in four humans does not have access to safe drinking water, with unsafe water being responsible for about a million deaths each year. Unsafe water can include water that is contaminated with infectious diseases such as cholera, with much of Africa and Asian countries like India heavily affected in this manner, but even wealthy countries like the US seeing its share of drinking water contamination incidents, with that of Flint, Michigan, being just one of many.

Such forms of contamination and lack of access to safe drinking water are obviously issues that ought to be resolved and prevented as well as possible once the cause has been determined. These days we don’t necessarily have to rely on constructed wetlands courtesy of modern technology, but they could be very beneficial as a self-sustaining water purification system.

As the US Geological Survey (USGS) points out, we are dealing with increasing drought since 2000 as well. This doesn’t merely translate into less rain, but also changes in the rain and melting patterns, as well as the availability of groundwater. This becomes apparent in periods of extreme drought interrupted by extreme rain accompanied with floods. As this makes water availability less predictable for drinking water and agriculture, the creation of reservoirs may be advisable, both to reduce the impact of floods and as buffers for dry periods.

Today we have many reservoirs that were formed due to dams blocking the course of rivers, but something similar could be done for rainwater, not unlike historical cisterns that once used to be extensively used throughout the world, like the famous Basilica Cistern below the city of Istanbul. It’s perhaps ironic that many of such cisterns were abandoned over the years, even as the need for them becomes more apparent today.