We recommend these sites:

Environmental Expert S.L.
Environmental Expert connects over 1,000,000 environmental industry professionals from around the globe to 20,000 companies that provide the products, services and information they need to do their job successfully. http://www.environmental-expert.com/

Environmental Equipment Engineering, Inc.
Environmental Equipment Engineering, Inc. manufactures floating aerators of unsurpassed durability and performance.
http://www.eeeusa.net/water-aerator.html

Mettler - Toledo Intl. Inc
Manufactures a complete line of pH, Redox, and dissolved oxygen systems including sensors, stationary and retractable housings, microprocessor-based transmitters, and conductivity and turbidity systems.
http://us.mt.com/us/en/home.html

International Water Association (IWA)
International Water Association (IWA) IWA's vision is to be the leading international membership association for the improvement of urban water management worldwide in an environmentally sustainable way.
http://www.iwahq.org/