A/HRC/6/3 page 12 2. Water quality 16. International declarations, resolutions and plans of action that include commitments to expand access to water also encompass specific quality requirements. Various instruments refer, alternatively, to clean water, drinking water, clean drinking water, safe drinking water, potable water, safe water, safe and clean water, or fresh water. According to CESCR general comment No.15, water for personal and domestic uses must be safe, therefore free from substances constituting a threat to a person’s health. Access to adequate sanitation constitutes one of the principal mechanisms for protecting the quality of drinking water.34 The Sub-Commission’s guidelines also mention that water must be of a culturally acceptable quality. 17. The WHO Guidelines for Drinking-water Quality (the WHO Guidelines) constitute an international reference point for drinking water quality regulation and standard setting. They define safe drinking water as water that does not represent any significant risk to health over a lifetime of consumption and that is free of microbial pathogens, chemical and radiological substances.35 These requirements apply to all sources of water provision.36 B. The meaning and scope of sanitation 18. Human rights instruments offer little guidance as to the scope and content of the term “sanitation”. The Sub-Commission’s guidelines refer to a right to sanitation, defined as the right of everyone to have access to adequate and safe sanitation that is conducive to the protection of public health and the environment.37 Accordingly, sanitation and sanitation facilities should be physically accessible, affordable, of a sufficient and culturally acceptable quality and in a location where physical security can be ensured. 19. Overall, human rights instruments refer to various concepts to describe the kind of sanitation facilities people should have access to and do not elaborate upon the specific requirements these various concepts carry. As such, the contour of the human rights framework for sanitation remains imprecise. The Sub-Commission’s guidelines alternatively refer to adequate, basic, acceptable and appropriate sanitation of a culturally acceptable quality without clearly defining what these various requirements mean and encompass and what the differences 34 The absence of sanitation systems in many parts of the world has led to widespread pollution and contamination of water sources that individuals rely upon for survival. 35 Guidelines for Drinking-water Quality, WHO, available at: http://www.who.int/water_ sanitation_health/dwq/guidelines/en/. 36 These include not only piped water sources, but also tanker sources, vendor-provided water and protected wells. 37 See E/CN.4/Sub.2/2005/25, para 1.2.