The ship, carrying water from nearby Tarragona, arrived Tuesday morning. A second vessel from Marseille, France, is scheduled to arrive Thursday.
The regional government of Catalonia, of which Barcelona is the capital, said 10 shiploads will arrive every two months, half from Marseille, the rest from Tarragona and Almeria, in southern Spain.
"The shipments are stopgap measures to avoid restrictions until a desalination plant is finished," said a spokeswoman.
The official could not be identified because of local government regulations.
The ship was carrying some 20,000 cubic meters (5.3 million US gallons) of water, roughly enough to satisfy a day's requirements for 180,000 people.
Spain is suffering its driest spring since records began 60 years ago. Catalonia is one of the worst-hit regions, with reservoirs at about a fifth of their capacity, compared with reservoirs on average half-full nationally.
With no rainfall in sight, authorities fear the reservoirs could drop to 15 percent of their capacity, a level at which it is no longer recommended that water be used for human consumption.
Authorities hope a new desalination plant - one of the biggest in Europe - will be operational next May and will resolve much of Catalonia's water woes.
The 5 million people living in the greater Barcelona area use 1 million cubic meters (264 million gallons) of water a day. The ship imports are expected to provide the equivalent of less than three days water a month.
With the busy summer tourist season ahead, the region has been moving frantically to avoid serious cuts in supply. Already city fountains and beach showers have been turned off and restrictions placed on filling large swimming pools.
Last month, it reached an agreement with Spain's central government for a temporary water transfer from the Ebro River.
The Socialist government in 2004 scrapped plans by their conservative predecessors for a permanent, major water transfer from the Ebro to the southeast regions of Valencia and Murcia. Both areas are run by the conservatives and live off mass tourism and agriculture.
The Socialists promote desalination plants as a way to solve the problem and say regions should live with the water they have. But the agreement to help Catalonia with the latest transfer, although infinitely smaller in comparison, has enraged Valencia and Murcia.
