WATER SAVING ASSESSMENT IN RESIDENTIAL BUILDINGS

Water is a common good essential to the survival of living beings, it is a finite resource that affects more and more the economic and social development of mankind, as has been clearly underlined by the World Conference in Johannesburg (August 2002). To support the growth of the world population, that has already exceeded 6 billion of people, humanity has to deal with the industrial development within a significant increase in social and economic conditions.
The WHO (World Health Organization) has estimated that the consumption of 100 cubic meters /year of water per person is the limit below which it is impossible to have economic development and ensure the health and welfare of people.
97.5% of the total reserve of water on the planet is salt water, only 2.5% is fresh water, of which 70% is frozen in ice caps, and the remaining 30% is made up of surface rivers or underground deposits. The scarcity of water resources is so important that it is placed at the center of research programs around the world. The data on current and future (up to 2025) water availability in the Mediterranean countries show a worrying reduction of available water resources, which in thirty years (1960-1990) have more than halved. Critical situations (average quantities available around 0,5 m3/day of water per person) are already present in 1990 in 4 countries (Libya, Malta, Saudi Arabia and Yemen), to become seven in the 2025 projections 2025 (the countries already mentioned plus Jordan, Syria and United Arab Emirates). However, in the forecasts for 2025, only six countries out of 17 will have an average availability of over 1 m3/day per person, including water for agricultural use. [1] 

Domestic Water consumption
The domestic water consumption represent one of the most costly in the balance of consumption of drinking water on the planet, since the vast majority of homes are equipped with a single distribution system, which feeds all devices with drinking water, even for uses in which it is not required. The graph in Figure 1 shows how much of the water used in the houses could be replaced by water recovered from purification systems of the rain or waste gray water treatment. 

The Italian situation
The reference standard for the supply of water to the population indicates that the manager of the water service is required to provide to the users the minimum levels of service and to ensure a budget per capita daily not less than 150 liters per inhabitant per day, meaning volume attainable by the user within 24 hours (dPCM 04/03/96, n. 46). The analysis of the consumption of drinking water billed per capita allows to detect the amount available for each inhabitant, while identifying trends in the behavior of citizens in the use of water resources.
On average in the provincial capitals water consumption per capita in 2011 amounted to 175.4 liters per inhabitant per day, 3.7 percent less than in 2010; in the long-term decline was slightly less than 15 percent (it was 206.1 liters per capita per day in 2002).