present, the amount of “newly developed”
water sources accounts for 16.6 billion m3 of
water per year, which amounts to 55% of
total water consumption for domestic and
industrial (urban) use 3 (See Figure 2-1). In
the Tokyo metropolitan region the volume
of bulk water stored in reservoirs doubled
from 185 million m3 in 1964 to 371 million
m3 in 1996. In 1996, water supply was
restricted for only 41 days, although annual
precipitation in 1996 was lower than in 1965
(a major drought year) and Tokyo’s
population had increased from 8 million to
11 million between 1965 and 1996.
As in many countries, agricultural water
accounts for about two thirds of total water
consumption, largely because of the huge
irrigation needs for paddy rice cultivation.
However, this does not necessarily mean
that agricultural water is used inefficiently.
Irrigation water is transferred from one
place to another and used repeatedly.
Except for limited evapo-transpiration of
water, most of the water used in irrigation
is returned as either return flow to rivers or
canals or as recharge to the ground water
aquifer. In recent years, the demand for
agricultural water has tended to decrease
due to the decrease in the area of irrigated land
used for the production of paddy.
Industrial water use has also tended to decline,
not only because Japan has suffered from
sluggish economic growth, but also because
the recycling rate has steadily increased.
Firms have learned to use their own