TOKYO - Japan's trading houses see water as their next big investment target as industrialization and rapid urbanization in emerging economies boost demand for clean water.

Following are the world's top-5 water service companies.

Company Customers*

1. Veolia Environnement SA (France) 139

2. Suez SA (France) 120

3. RWE AG (Germany) 38

4. Aguas Barcelonas (Spain) 30

5. United Utilities Plc (UK) 24

* No. of customers for drinking water services in millions

Source: Marubeni Corp

(Reporting by Yuko Inoue, Editing by Ian Geoghegan)