Climate change is a serious problem facing almost all the inhabitants of the Earth. They are already present and are manifested in rising temperatures, rising sea levels, melting snow and glaciers and changing precipitation patterns. It is very likely that the cause of most warming lies in the observed increase in the concentration of greenhouse gases, which is the result of human activities. To mitigate climate change, we must reduce or prevent those emissions. Due to the uneven distribution of water on Earth and climate change, we observe phenomena such as drought, floods, storms, which in turn lead to population migrations, economic crises and wars. Climate change is manifested primarily in the atmosphere but is closely linked to developments in the entire Earth system, which in addition to the atmosphere includes oceans and other waters, ice cover, soil and wildlife. Climate change and water are inextricably linked and this paper will demonstrate the interconnectedness as well as the importance of conserving water resources and their impact on sustainable development. Extreme weather and rain are becoming more common in some regions, while intensified waves of heat and drought are occurring in others. These effects are expected to intensify in the coming decades. As a result, the costs of developing water technologies are rising and increasing differences are being created in the possibilities of using geostrategic water resources. This paper will show how climate change affects water availability in large cities on the example of Barcelona and Athens, but also how they deal with these problems and how they solve them.