Are Earthquake-Resistant Water Pipes Also Good for Water Taste?
Japan's water pipes are only 42% earthquake-resistant. The choice of pipe material affects not only earthquake resilience but also the taste of tap water.
Japan's Water Pipe Earthquake Resistance Rate Still at 42%
According to the latest survey by the Ministry of Health, Labour and Welfare (FY2022), the earthquake resistance rate of key water pipelines nationwide is only 42.3%. This is significantly lagging behind the national target of 60% or higher by the end of FY2028. In an earthquake-prone country like Japan, water outages directly impact lives, making the selection and replacement of pipe materials an urgent issue.
Differences in Water Pipe Types and Earthquake Resistance
The earthquake resistance of water pipes varies greatly depending on the material and joint structure.
Cast Iron Pipes (Grey Cast Iron Pipes) — A historic pipe material used since the Yokohama City water system in 1885, but it is hard and brittle, making it easy to fracture during earthquake tremors. New installations are now prohibited, and they are targeted for replacement.
Rigid Polyvinyl Chloride Pipes (VP Pipes) — Inexpensive pipe material that supported the post-war expansion of water systems. However, they have low flexibility, and a large number of disconnections and fractures were confirmed during the Great Hanshin-Awaji Earthquake (1995), bringing their low earthquake resistance back into focus.
Ductile Iron Pipes (GX/NS Joint Types) — The current mainstay of key pipelines. The nodular graphite structure provides high impact toughness, and a lock ring inside the socket prevents the pipe from pulling out due to ground deformation. They also have high corrosion resistance due to internal epoxy powder coating or cement mortar lining.
Polyethylene Pipes for Water Distribution (PE Pipes) — The pipe material with the highest level of earthquake resistance today. Since the pipes and joints are integrated by electrofusion, joint disconnection is unlikely to occur. They have a track record of virtually zero damage in the Niigata Chuetsu, Great East Japan, and Kumamoto earthquakes, and their adoption for small-diameter distribution branch pipes is expanding rapidly.
Actually Directly Linked to "Water Taste"
Pipe materials affect not only earthquake resistance but also the taste of the water we drink daily. In old iron and steel pipes, chlorine in the water accelerates rusting, causing a rusty smell and metallic taste. Anyone who has experienced reddish water coming out first thing in the morning has seen this exact phenomenon.
On the other hand, polyethylene pipes do not corrode and have extremely low leaching, making water quality more stable. Ductile iron pipes are also designed with internal linings so that water does not come into direct contact with metal.
Note that if you notice a "chlorine smell," it is caused by the residual chlorine used for disinfection rather than the pipe material, which is a separate issue. However, as pipe materials age, the rust smell combines with it, deteriorating the flavor. Upgrading to earthquake-resistant pipes also leads to better-tasting water.
Summary
The level of earthquake resistance is generally ranked as "Polyethylene Pipes ≧ Ductile Iron Pipes (GX Type) ＞ PVC Pipes ＞ Old Cast Iron Pipes." In areas with many aging pipes, keeping an eye on the progress of pipe replacement relates to both the risk of water outages during emergencies and the daily taste of water.
[Reference Materials]
Ministry of Health, Labour and Welfare "Status of Earthquake Resistance in Water Supply Businesses (FY2022)" https://www.mhlw.go.jp/stf/newpage_38800.html
Ministry of Land, Infrastructure, Transport and Tourism "Promotion of Earthquake Resistance in Water Supply Facilities" https://www.mlit.go.jp/mizukokudo/watersupply/stf_seisakunitsuite_bunya_topics_bukyoku_kenkou_suido_taishin_index.html
Tokyo Metropolitan Waterworks Bureau "Earthquake Resistance of Water Pipelines" https://www.waterworks.metro.tokyo.lg.jp/suidojigyo/suidoukanro10