Moss Foundry and Engineering Works is founded by Matthew Mills and later taken over by James Mills.

Thomas Hawksley becomes a member of the Institution of Civil Engineers.
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Hawksley was one of the greatest 19th century water engineers. In his lifetime, he achieved international recognition for developing the first pressurized clean water supply available at the turn of a tap. This system saved countless lives when cholera struck Great Britain in 1848 and is one of the reasons the country’s health and prosperity accelerated ahead of many others in the following decades.

The T&C Hawksley international engineering partnership between Thomas Hawksley and his son, Charles Hawksley is established.

John Duncan Watson began his revolutionary career in water and wastewater treatment with an appointment as Borough Surveyor. His notable achievements included the construction of the first large percolating filter plant, abandoning traditional methods for more innovative techniques. Other radical changes that he led were the recovery and utilization of methane for energy in gas engines, separate sludge digestion, and two-stage purification of tank effluents by primary flocculation prior to percolating filter treatment.

The son of James Mills, Matthew William Mills, who later became a leading authority in sewage machinery, revives Moss Foundry and Engineering Works under the name of James Mills and Company, Ltd.

Matthew William Mills, son of James Mills, of James Mills and Company, Ltd. files a patent for a new type of machinery for the activated sludge process, used in the mechanical aeration of sewage. The process was afterwards very widely adopted.

Harza Engineering Company, which offered energy and environmental engineering services is founded by Leroy F. Harza

Ames Crosta Mills and Company, Ltd. is formed for developing the sales of sewage purification machinery patented by James Mills and Company, Ltd. Matthew Mills is one of the original directors.

The JD & DM Watson partnership between the retired John Duncan Watson and his son David M. Watson is formed for municipal wastewater treatment.

Ames Crosta Mills and Company, Ltd. manufactures the simplex sewage purification plant that drives the modernization of environmental standards for wastewater treatment and for mechanical aeration products used in the activated sludge process, still in use today.

James M. Montgomery (JMM), an environmental engineering consultancy firm specializing in water and wastewater, is established by James McKee Montgomery and begins to offer construction management services. JMM is later incorporated in 1954.

Methuen Construction Company was founded in 1960 by Leon and Elizabeth Asadoorian. The Company had its origins in residential and commercial site construction. In the mid 1960's Methuen began serving private utility companies throughout the Merrimack Valley of Massachusetts and New Hampshire. This is the original office at 90 North Lowell Street in Methuen, MA.

Biwater Treatment Company, Ltd. is formed by Sir Adrian White, establishing themselves as pioneers in the field of water, wastewater and sludge treatment.

Ames Crosta Mills and Company, Ltd. is briefly absorbed by Babcock and Wilcox, Ltd. (est. 1867) and renamed as Ames Crosta Babcock, Ltd.

JD & DM Watson and T&C Hawksley merge to form Watson Hawksley, Ltd.

Slayden Construction Group, Inc. is established, focusing on water and wastewater construction projects in the Pacific Northwest.

Biwater Treatment Company, Ltd. acquires Ames Crosta Babcock, Ltd.

JMM merges with English firm, Watson Hawksley, Ltd. to become the global environmental engineering firm of Montgomery Watson, Inc.

Montgomery Watson Constructors, Inc. is established as the construction company with Montgomery Watson, Inc. for construction management-at-risk and alternative delivery contracts for municipal and federal clients.

Montgomery Watson, Inc. merges with Harza Engineering Company to create global energy, utility, and environmental engineering company known as MWH Global, Inc.

Montgomery Watson Constructors Inc. becomes MWH Constructors, Inc.

MWH Constructors, Inc. acquires leading UK water construction and engineering firm Biwater Services Ltd., to form MWH Treatment, Ltd.

MWH Constructors, Inc. acquires Slayden Constructors, Inc.

MWH acquires Methuen Construction Company, a self-performing general contractor with more than 60 years of experience in the Northeast.

MWH enters an agreement to join forces with Obayashi Corporation, a global leader in construction with a rich history dating back to 1892 based in Tokyo, Japan.