Given Malta's lack of permanent freshwater rivers and limited rainfall, what methods did the ancient Maltese use to obtain potable water?

A post on Reddit on r/geography asked how the Maltese people historically managed their water needs, given the island's water scarcity. The question sparked an answer by a Maltese historian (u/bertthemalteser) who provided an overview of the traditional water management techniques used on the island. I'm reproducing his reply in full:

"Hi! I'm a Maltese historian! This is a really fascinating part of our history and a really important part of how our country developed.

We know through archaeological findings that the first settlers could rely on the very few natural springs that there are, but then identified the qualities of Maltese geology - which is largely characterised by limestone - to excavate cisterns for rainwater collection and water storage. Megalithic temple complexes which date back over 5,000 years have rock-cut cisterns, for instance.

Malta today has no permanent above-ground freshwater supply to speak of - certainly no rivers or lakes; but the key lies in what is beneath. Groundwater is basically the only year-round permanent supply of fresh water, and this is what was used in ancient times - and is still used today to some degree - for the population to supply.

You've got two types of groundwater: the perched aquifers in western areas of the island, which geographically are situated higher than sea-level than other parts of the island, and sea level aquifers.

Perched aquifers were more limited in groundwater quantity, but were at a much more shallow level than those at sea-level - which on the other hand were more difficult to exploit owing to their depth, but had a lot more potential.

Later in history, water supply remained a key part of how Malta was shaped. The Arabs (appro 870AD to 1091AD) for instance are credited with introducing a lot of techniques to conserve water. For instance, we have records of how major villages were located next to newly identified natural water sources, and close to wells or cisterns. Analysis of place names from back then for example shows that there were 137 places with the word 'Bir' - which translates to 'Well' even in today's Maltese language - and another 87 with the word 'Ghajn' - which translates to spring - in their names.

Farmers used various techniques even for irrigation, including the manual digging of vertical shafts known as 'spiera' to reach groundwater and then using an animal driven water wheel - called a 'sienja' (the j is pronounced as a y) - to get water to the surface.

Water continued to be an important factor later: for example, when the Knights of St John constructed what is today the country's capital city of Valletta, there was an express order that every single dwelling in the fortified city must have a well and no house could have a garden, so to reduce water consumption.

The Knights also commissioned a system of aqueducts in the early 1600s to supply the new capital and the towns around it. Plenty of those aqueducts and the monuments are still standing today, although not in use.

The British who came to Malta in 1802 had to contend with increasing populations, and therefore increased water usage, and in 1851 the industrial revolution was harnessed through the use the first motorised pump system on the island in order to - for the first time - use the sea level aquifers in an organised manner. Spectacular reservoirs were constructed for water storage, while pumping stations also started to be built together with more modern pipelines to connect more and more areas.

In 1881 technology allowed the first sea water distillation plant - a boiling-type plant - to be built in order to purify sea water - another significant milestone.

Today, Malta relies on reverse osmosis for its water supply - a plant built in 1982 was for a time the biggest in the world in fact - and there's a number of these plants in operation today, meaning that problems - at least for the common people - of water supply are a thing of the past.

If you're a real water history nerd, I recommend the recent publication 8,000 Years of Water which is dedicated only to this subject!"