"Would you like some water? Turn off the tap!" one public service announcement in Athens implores; another daily spot urges the capital's residents to not fill their bath all the way to the top.
Already, there are signs that habits may need to change.
At the beginning of July, the Mornos reservoir around 200 kilometres (125 miles) west of Athens, the main water source for the Attica region surrounding the capital, levels were down 30 percent from the same period last year.
And overall reserves for Attica were down by nearly a quarter over the same period, according to the water utility company EYDAP.
Home to more than a third of Greece's population, the region of 3.7 million inhabitants was recently placed on "yellow alert" by EYDAP, which urged people to reduce consumption to keep reserves at a sustainable level.
Overtourism, poor management
Across Greece's islands, which tend to rely on wells and desalination plants to meet water needs, the problem is even more acute.
Added pressure comes from the millions of tourists who flock to the country's beaches each summer, swelling the local populations.
On some islands suffering from overtourism, the demand for water in summer "is sometimes 100 times greater than in winter", Nikitas Mylopoulos, a professor of water resource management at the University of Thessaly, told AFP.
Mylopoulos said the problem of mass tourism was being compounded by poor water management.
At the end of June, a month-long state of emergency was declared for the Dodecanese island of Leros.
The island's council noted malfunctions at the desalination plant, alleging "poor maintenance in the past".
Other islands threatened by water scarcity include Sifnos in the Cyclades, Chios in the north Aegean and Lefkada and Corfu in the Ionian Sea.
Sifnos's mayor, Maria Nadali, has criticised "the over-consumption of water for swimming pools and watering large gardens".
On Lefkada, Michalis Makropoulos, a local resident and author, denounced a "deplorable" situation where "the water was cut off at the end of June for four consecutive days".
In a local newspaper article, he blamed the problem on "years of mismanagement by the municipal authorities" and the "uncontrolled development of tourism without adequate infrastructure".
Prime Minister Kyriakos Mitsotakis travelled to Lefkada in July to announce "one of the largest water supply projects in Greece to cover the needs".
Extreme weather
The water shortfalls have been made worse by intense heat, which scientists say is at least in part a result of human-driven climate change.
The mildest Greek winter on record has been followed by higher average temperatures this spring.
Last month, the country's earliest-ever heatwave resulted in the hottest June since 1960, with temperatures reaching 43 degrees Celsius (109 Fahrenheit) in many parts of the country.
The heat has also sparked an increase in wildfires, with more than a thousand recorded last month, more than double the number in the same month last year, authorities say.
The head of the water utility EYDAP, Charalambos Sachinis, has said a "special plan" had been drawn up "to deal with extreme water shortages", including investments of around 750 million euros ($819 million).
Elissavet Feloni, a hydrologist at the National Technical University of Athens, said the company was also planning to tap Lake Yliki, around 85 kilometres northwest of Athens, as an additional emergency source alongside the main Mornos reservoir.
"However, this is an energy-intensive solution because the water has to be pumped up, whereas the Mornos stream has a natural gradient," she said.
"For better water management, a central body needs to be set up to develop a comprehensive approach to resources across the country," she said.
