This chapter addresses water security, which is a contested normative concept, without clear definitions, meanings, or interpretations. With this in mind, the term ‘water security’ must be understood in two distinct ways: security through water (meaning individuals’ access to water to sustain their lives and livelihoods) and security against water (meaning the absence of water-related threats, both natural and man-made). The concept of water security as security through water is a tool to guarantee certain minimum standards of water for individuals. This aspect of water security is closely related to the idea of a human right to water as derived from and related to other human rights such as the right to life, an adequate standard of living, and the right to the highest attainable standard of health. However, water can also pose threats. For instance, given its outstanding political and economic significance, the likelihood of ‘water wars’ has been discussed in international law and politics for some time. Special challenges to water security include the widespread privatization of water, climate change as catalyst for future water conflicts and water-related natural disasters, and the often forgotten ‘sanitation gap’.