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Water Treatment and Water Quality Management
Water Distribution Management

Water supply coverage is over 97% in Japan and it is common for people to drink directlyfrom the tap. This requires Japanese water utilities to provide safe and reliable water supply at
all times, and it is important to carry out appropriate water distribution management, such as
water volume and pressure adjustment and monitoring of distribution status.
1. Water distribution management
In Japan, water volume and pressure are adjusted to ensure equal and appropriate pressurein the service area. If the pressure or volume is insufficient due to the capacity of the distribution
pipes, it is necessary to set them according to the location and topography of the water source(s)and water treatment plant(s) as well as the water demand. In addition to equalizing the waterpressure and quality in the service area, the distribution system has been divided into
appropriate-size distribution blocks in terms of both land area and elevation in order to makethe water volume and pressure control easier.
(1) How to set up water distribution blocks
In general, there are two types of distribution blocks: “distribution main blocks" that consistof distribution reservoirs and distribution mains, and "distribution submain blocks" that consistof distribution submains branching out from distribution mains. For small water supply systems
without a complicated distribution network, it may be more rational to set up zones according
to land elevation or to partially increase or decrease pressure according to the zones, rather
than dividing the system into distribution submain blocks. The following is a basic way to set up
distribution submain blocks.
① When water distribution mains are used for mutual water accommodation, they shouldbe used as normal distribution pipes as much as possible during non-emergency to avoid
water stagnation inside the pipeline.
② The size of distribution submain blocks should be determined based on the area’s
population, existing distribution submains, and the shape of roads. The number of
injection points from the distribution mains to the distribution submains should be twoto three, considering the block size and emergency response for injection points, so as toensure and facilitate the management of water volume, pressure, and quality.

様式〔概要〕Distributionreservoir “A”

Reservoircommunication pipe

Distribution
main

Distribution
reservoir “B”

Blockboundary

Distribution submain block

Block “A”

Figure | Relationship between a distribution main and distribution submain block
Furthermore, to provide safer and better-quality tap water, there is a need to strengthen the
total water quality management from source to tap. To do this, water utilities are using
automatic water quality monitors (for color, turbidity, residual chlorine, pH, electricalconductivity, water temperature, pressure, etc.) and ultra-compact automatic water quality
measuring devices to monitor the water distribution status. Also, they consider downsizing thepipeline capacity when it is likely to cause water stagnation inside it, which can deteriorate
drinking water quality.
2. Case studies(1) Efforts to prevent turbid water (Yokohama City Waterworks Bureau)
The City of Yokohama has provided guidance on wastewater discharge to each of its businesssite to prevent water pollution in public waters based on the Water Pollution Control Law and
the Yokohama City Ordinance on the Preservation of Living Environment.
(2) Water pressure control using the distribution block systemTo be published together with relevant case studies in future (publication date TBD)
(3) Strengthening water quality monitoring at the customer tap (use of automatic water qualitymonitors)
To be published together with relevant case studies in future (publication date TBD)
References2