The Roman engineer and architect Marcus Vitruvius Pollio (c. 75 B.C.–c. 15 A.D.) wrote an extensive and invaluable work (De Architectura) that describes all types of topics in construction and building. We will here describe his interesting (and somewhat amusing) method of locating water springs. This information can be found in book VIII, ch. 1 of his treatise.
He begins with the obvious:
[Aqua] est enim maxime necessaria et ad vitam et ad delectiones et ad usum cotidianum.
“Water is of course absolutely necessary for life, enjoyment, and daily use.” The first step in locating water is to get a good look at the terrain. This may be accomplished, he tells us, by laying down on the ground before sunrise and resting one’s chin against the ground, and directing the eyes this way and that. In this way the observer will have a clear and fixed line of sight on the surrounding terrain, and will be able to spot uneven ground. He will also be able to observe water vapor rising from the ground; here is where digging should be considered.
Different types of ground sediment will have different locations for water. In clay, the water is normally not near the surface and may be bad for drinking. The same holds true for loose gravel (Item sabulone soluto tenuis). The best water seems to come from areas with hard rocks or near the bases of mountains. In general, springs found on too level ground are excessively mineral and “unpleasant” (non suavae). Also to be avoided if possible is water coming from marshy areas, presumably because of its stagnant qualities.
Water coming from the mountains he values most highly of all. The same could be said of us today. He says mountain water is better, more wholesome, and more pure than other types.
When a water source has been located, Vitruvius advises the following method of extracting it. A hole should be dug about 3 feet square and five feet deep. At sunset, the prospector should place a vessel (or basin) made of bronze or lead in the hole, inverted so it is facing down. The inside should be thoroughly rubbed with oil. The hole should then be covered over with twigs or leaves, and excavated earth placed on top of this.
Re-open the hole the next day, he advises. If drops of water have condensed or appeared inside the oil-smeared vessel, then water will be found in this spot.
The same ritual can be duplicated if a “fleece” or roll of wool is used in the hole instead of an inverted metal basin. A vessel made of clay would not work well unless it is fired in a kiln; otherwise it will absorb moisture and the prospector will not be able to tell if drops of water have collected. Another way to discern water is to light a small fire in the hole; if water vapor rises from the hole continuously, then this may be a good indication of water being there.
Once a decision has been made to dig a well, it is better to dig several shafts close together in roughly the same area, and then to connect those wells into one place using separate channels (plures circa sunt fodiendi et per specus in unum locum omnes conducendi).
These are some of Vitruvius’s interesting thoughts on water prospecting.