 Finally, it also states that recreational or free areas must be covered with permeable materials.Past responses to the water challenges facing Greater Mexico City included an ambitious water conservation campaign initiated in 1989, as well as an increase in metering and a reduction in leakage through private sector participation begun in the early 1990s.In 1989, in parallel with the introduction of stricter national water efficiency standards for household appliances, Mexico City launched an ambitious program to replace conventional toilets (using 16 liters) with 6-liter models, replacing 350,000 toilets by 1991.