Yokohama's waterworks system was the first modern such system to be built in Japan, and began supplying water in 1887. Although Yokohama was a small community with less than 100 houses at the time, the ensuing 120 years saw a series of eight projects for expansion of the system to meet the demand for water, which steadily grew along with the city. As a result, by 2009, the system was supplying water to 100% of the population and more than 1.75 million houses.
Modern sewerage took its start from the sewers laid in Yokohama's foreign settlementway back in 1861. The sewage system was expanded at a fast rate to cope with the rapid population increase beginning in 1965. Over the 15-year period beginning in 1980, the city made huge expenditures of about 100 billion yen per year and 1,900 billion yen total, for a dramatic increase in the sewered population, which reached 99.8% in 2010.
Yokohama is working to maintain a sound water cycle stretching all the way from headwaters to return to the sea. The key technology and know-how are as follows.
For sustained supply of high-quality water indispensable to the city, Yokohama acquired a 2,800-hectare riverhead area in the village of Doshi, Yamanashi Prefecture at an early date (1800), and has continued to manage the headwaters forest there.
Referred to as "green dams", forests in source areas fully absorb rainwater, purify it, and transform it into high-quality groundwater. They also act to allay inundation and prevent drought.
To prevent proliferation of algae on lakes, Yokohama has installed aeration units that circulate the water.
The high quality of Yokohama's water has made it the focus of worldwide attention. Seaman say that it stays fresh even after being carried across the equator.
Yokohama boasts a water supply system with an extended pipeline length of 9,200 kilometers from the collection to the supply ends, and a leakage rate of just 5.4% (as of 2010). The share of the city population supplied by the system reached 100 percent in 1989. The system facilities continue to be properly maintained and managed, for stable supply of safe water people can drink and use with complete peace of mind.
In consideration of the its seven rivers and terrain, Yokohama was divided into nine districts for performance of wastewater treatment and stormwater management.
Yokohama's sewage system currently consists of sewer pipes with an extended length of about 11,600 kilometers as well as 11 water reclamation centers and 26 pumping stations. It treated about 640 million cubic meters of wastewater in fiscal 2008. The sewage sludge derived in the treatment process is sent by pipeline to the two sludge resource centers in the city for incineration. Effective use is made of the entire amount of ash from sludge incineration, which comes to about 17,000 tons per year.
As one of its measures implemented in recent years to prevent global warming, Yokohama has also been working to reduce CO2 emissions by turning sewage sludge into a fuel.
To Yokohama, effluent from advanced treatment of wastewater is a precious urban water resource, and is supplied to various locations in the city. Water is also treated for removal of nitrogen and phosphorus to prevent a worsening of water quality due to eutrophication on Tokyo Bay and other closed water areas.
Yokohama is determined to protect citizen lifelines and assure business continuity plan (BCP) in the event of disasters. To this end, besides implementing aseismic improvements in waterworks and sewage system facilities to curtail any damage they incur to the minimum, it is systematically promoting various initiatives to assure supply of drinking and other water needed for life activities, and sanitary living conditions at shelters.