Introduction
In 1996 and 2002 the first general studies of the water supply of Ostia were published. The first is the work of Scrinari and Ricciardi: "La Civilta dell'Acqua in Ostia Antica", Roma 1996. The more recent one was written by Gemma Jansen. Jansen's PhD thesis was published in Dutch: "Water in de Romeinse stad (Water in the Roman city): Pompeii - Herculaneum - Ostia", Leuven 2002. Subsequently research and excavations began by the French, by Bukowiecki and others. In 2020 Mark Locicero's PhD thesis about the water systems was published: "Liquid footprints: water, urbanism, and sustainability in Roman Ostia", Leiden 2020.
The raising of Ostia
For a study of Ostia's water supply the raising of the level of Ostia is a crucial background. In the east half of Ostia the following has been established, as described by Laura Sole:
- A raising of c. 0.70 on top of the sand. On this layer rest the so-called Cippi of Caninius, that have been dated by Meiggs to c. 150-125 BC.
- A raising of c. 0.80 on top of layer 1. On this layer rests the Republican Temple on the corner of Via dei Molini. This raising should probably be dated to the reign of Claudius.
- A raising of c. 0.15 on top of layer 2, probably from the reign of Domitian.
- A raising of c. 0.25-0.75 on top of layer 3, probably from the reign of Hadrian.
- A final, slight raising, probably Severan, taking the final level to c. 2.00-2.50 above the sand.
Jansen has established some remarkable facts about the raising of the late first and early second century AD. It was not a systematic attempt to increase the distance to the ground water or to the flood level of the Tiber. The raising did not lead to a flat surface, nor to a surface tilting to one side. There are great variations in the thickness of the raising. In any case, the raising necessitated a new system of water-supply and -drainage (lead and terracotta water pipes, sewers).
Ground water and rainwater
The ground water in Ostia was in antiquity at a depth of 2.5-4.5 metres. The quality is good and the source reliable. Therefore it is not surprising that many wells were made in the city. They have a masonry shaft, and a well-head (puteal) of masonry, terracotta or marble. Some could be closed off with a lid. Water was hoisted up using a bucket on a rope. Terracotta pipes leading to the shaft prove, that sometimes rainwater was led to the wells. However, the collecting of rainwater was exceptional in Ostia. Most of it was led away unused. In late antiquity, in a depopulated Ostia, wells were sometimes built on the middle of streets (Decumanus Maximus, Semita dei Cippi).
The ground water was also used in several baths, where it was taken to rooftanks by using waterwheels operated by slaves. The wheels were installed in narrow rooms. Sometimes holes can be seen in which the axes of the wheels were inserted, and on the walls traces of wear caused by the wheels. The wheels took the water to tanks on the first floor. In a few baths is a second wheel, taking the water to the second upper floor. A few clusters of tanks were found. Thick walls supported them. The inside of the tanks was covered with waterproof mortar (opus signinum). From the tanks the water was distributed through lead conduits or masonry gutters. The water-flow was controlled by taps. Some of these reservoirs supplied not only the baths, but also public fountains and private buildings, for example in the Terme del Foro.
The aqueduct and main distribution system
The supply was greatly improved by the building of an aqueduct in the early Imperial period. The aqueduct is described on a separate page. The water of the aqueduct was taken to the buildings in various ways. The distribution could take place entirely underground, through lead pipes, sometimes having taps. Often the pipes carry stamps referring to the owners of the workshops where they were made (plumbarii) or to the owners of the buildings. The main pipe was found below the eastern stretch of the Decumanus Maximus, with the stamp colonorum coloniae ostiense ("of the colonists of the colony Ostia"). It is at a depth of 0.7-1.8 m. below the street.
Sometimes the water was distributed further through a system of lead pipes branching off. In some cases the water was led to (clusters of) distribution basins above ground, comparable to those fed by water-wheels (examples in the Terme del Faro, Terme di Nettuno and above the public fountain in Via della Fontana). The pressure of the water necessitated very thick walls supporting the tanks, sometimes with buttresses. In the Terme del Faro and the Terme di Nettuno ridges were found that supported lead pipes leading to the final destination of the water.
The water supply of street fountains and buildings
As we have seen, the distribution reservoirs were filled with ground water and aqueduct water. From the reservoirs the water was led to 46 street fountains and 171 buildings (not counting baths) in the excavated part of Ostia.
A bronze tap for controlling the water flow in the lead pipes. Photo: Parco Archeologico di Ostia Antica.
Street fountains could be simple basins, large basins covered by barrel vaults, and decorated nymphaea. The small basins are found typically near the entrance of baths and apartment buildings. A good example of a covered basin was found in Via della Fontana. Overflow holes in these basins prove that normally there was a continuous flow of water, with which buckets could be filled that were placed in shallow depressions. However, water was also collected directly from the basins, through a "window" in the front: traces of wear caused by ropes can be seen. This suggests that sometimes the flow of water was interrupted, albeit not for a long period of time, because the reserve in the basins was small. This in turn suggests that the flow was regulated, because there was (just) not enough water available. Perhaps the water-supply of alternating parts of the city was interrupted for a few hours each day. The nymphaea are found along main streets and on squares. They adorned the city, but had a practical purpose as well: water could be collected from their overflow basins.
The types of connected buildings (excluding the baths) are listed below:
| Type of building | Number of buildings | Total number of water outlets |
| Apartment buildings | 21 | 37 |
| Religious buildings | 8 | 11 |
| Guild seats | 4 | 11 |
| Houses | 27 | 38 |
| Commercial establishments | 106 | more than 150 |
| Other | 5 | 5 |
| Total | 171 | more than 252 |
The number of water outlets per building is small. However, one outlet could have several functions. It could, for example, supply a nymphaeum, the overflow water of which was led to a toilet. Commercial establishments (fulleries, bakeries, bars and so on) usually had several water outlets. The maximum number of outlets (seven) has been found in a guild seat, the Schola del Traiano. It has been suggested that there were also outlets on upper floors, in the luxurious apartments of the Case a Giardino.
Toilets
Toilets were found in 19 commercial establishments, usually below staircases. Toilets are normally present in the domus and medianum-apartments. Many communal toilets have also been found, either as separate units or incorporated in buildings such as baths and guild seats.
The Ostian toilets consist of seats with holes (for obvious reasons) and with a hole in the front, through which a sponge on a stick could be used. The sponges could be cleaned in a bucket, in a small basin, or in a gutter with running water in front of the seats. Urine and faeces were removed either by running water or manually, by using water in a bucket. The latter was done in small toilets only, that had an open front. The larger toilets were flushed with the water flowing through the gutter and with additional water coming from nymphaea, baths and so on.
Sewers
There were no cesspits in Ostia, due to the high level of the ground water. There is an extensive system of sewers below buildings and streets. The sewers can be traced and inspected through travertine and marble lids that cover vertical shafts leading to them (examples on the Decumanus near the Theatre, on the streets near the Bivio del Castrum and to the east of the Baths of Mithras). The sewers are rectangular tunnels (width 0.6-0.8 metres, height 0.6-1.4 metres). The side walls are made of opus latericium or opus reticulatum, the floors of terracotta tiles. They are covered by gable roofs or barrel vaults. They received the waste water from baths, commercial buildings, houses and toilets, the overflow water from nymphaea and basins, and rainwater. Water was led from the roofs of buildings to the sewers through vertical terracotta pipes, usually embedded in grooves in the wall, and then through horizontal terracotta channels. The water that was used for cleaning the floors was led to the horizontal channels through small lids with holes in the floor. The only water on the streets was rainwater. Apparently this did not create problems, because sidewalks are low and there are no stepping stones as in Pompeii.
There are no great differences in height in the city (the maximum difference is 2.45 metres). Height measurements of the bottoms of the sewers have not yet been taken (the bottoms are covered with a thick layer of mud), so it is still not clear where the waste water was led to. Measurements of the streets have shown that the rainwater was not taken systematically to the Tiber or outside the city through the gates. It was taken to the sewers through lids with holes.
Reconstruction drawing of water supply and a sewer.
From A. Pascolini, Ostia, Roma 1979, p. 29.