The marches were part of the first co-ordinated effort by activists concerned with the ills of overtourism across southern Europe's top destinations.
"The squirt guns are to bother the tourists a bit," Andreu Martínez said in Barcelona with a chuckle. "Barcelona has been handed to the tourists. This is a fight to give Barcelona back to its residents."
Barcelona hosted 15.5 million visitors last year eager to see Antoni Gaudí's La Sagrada Familia basilica and the Las Ramblas promenade.
Martínez says his rent has risen over 30 per cent as more apartments in his neighbourhood are rented to tourists for short-term stays.
He said there is a knock-on effect of traditional stores being replaced by businesses catering to tourists, like souvenir shops, burger joints and "bubble tea" spots.
"Our lives, as lifelong residents of Barcelona, are coming to an end," he said. "We are being pushed out systematically."
Around 5000 people gathered in Palma, the capital of Mallorca, with some toting water guns as well and chanting "Everywhere you look, all you see are tourists."
The tourists who were targeted by water blasts laughed it off. The Balearic island is a favourite for British and German sun-seekers. Housing costs have skyrocketed as homes are diverted to the short-term rental market.
Hundreds more marched in Granada, in southern Spain, and in the northern city of San Sebastián, as well as the island of Ibiza.
Cities across the world are struggling with how to cope with mass tourism and a boom in short-term rental platforms, like Airbnb, but perhaps nowhere has surging discontent been so evident as in Spain, where protesters in Barcelona first took to firing squirt guns at tourists during a protest last summer.
Spanish authorities are striving to show they hear the public outcry while not hurting an industry that contributes 12 per cent of gross domestic product.
Last month, Spain's government ordered Airbnb to remove almost 66,000 holiday rentals from the platform that it said had violated local rules.
Spain's Consumer Rights Minister Pablo Bustinduy told The Associated Press that the tourism sector "cannot jeopardise the constitutional rights of the Spanish people," which enshrines their right to housing and well-being.
Carlos Cuerpo, the economy minister, said in a separate interview the government is aware it must tackle the unwanted side effects of mass tourism.
The boldest move was made by Barcelona's town hall, which stunned Airbnb and other services who help rent properties to tourists by announcing last year the elimination of all 10,000 short-term rental licences in the city by 2028.
Txema Escorsa, a teacher in Barcelona, doesn't just oppose Airbnb in his home city, he has ceased to use it even when travelling elsewhere, out of principle.
"In the end, you realise that this is taking away housing from people," he said.
