The northern regions are especially vulnerable, the head of the ANBI water-resource consortium said on Thursday.
"According to the data we have available, it is reasonable to believe that the tap water of at least 3.5 million Italians cannot be taken for granted," ANBI President Francesco Vincenzi said.
He referred to data by the National Research Council (CNR), which indicated that between 6 per cent and 15 per cent of the Italian population are living in areas exposed to severe or extreme drought.
Low levels of rain and snowfall this winter has exacerbated an already difficult situation after the severe drought and long series of heat waves Italy endured last summer hit its water resources badly, causing huge problems for agriculture.
ANBI said the level of the Po, Italy's biggest river, was at a record low.
It said rivers and lakes in central Italy were also under extreme stress.
ANBI's warning comes after environmental association Legambiente sounded the alarm about the drought on Monday.
Citing figures from the CIMA Research Foundation, it said the Italian Alps currently have a snow-water-equivalent deficit of 53 per cent compared to the average of the last ten years.
This is of great concern, as the melting snow is an important source of water in spring and summer.
This deficit is due to reduced precipitation levels this winter, combined with mild winter temperatures that have brought forward the melting of snow on the mountains.
Alpine snow is Italy's most important water reserve, since it supplies the Po River basin.
Scientists say that extreme weather events like heatwaves, supercharged storms, flooding and droughts are becoming more frequent and more intense because of climate change caused by human greenhouse-gas emissions.
ANSA
