6.
safe water and toilets around the world Goal 6 is "Ensure the availability and sustainable management of water and sanitation for all". 
Image from the United Nations Information Center website (https://www.unic.or.jp/activities/economic_social_development/sustainable_development/2030agenda/sdgs_logo/sdgs_icon/).
a concrete urban problem
1.Aging, maintenance and renewal of water supply and sewerage systems
2.Wastewater treatment (Plants and agriculture and livestock industries)
The issue is quoted from the Ministry of Land, Infrastructure and Transport "Toward Smart Cities: [interim report] (https://www.mlit.go.jp/common/001249774.pdf)".
