"He has come to the conclusion that family must come first and he's choosing to step back into his project management roots so that he can spend more time with his children."
Williams was appointed as chief infrastructure officer after an independent report into Wellington Water and Wellington City Council found their relationship was lacking trust and in need of a "fundamental reset".
The role is responsible for the working relationship with Wellington Water.
The report was commissioned in December 2019 by McKerrow, as incoming WCC chief executive, who was alerted to issues with the working relationship.
The report said disagreements between the two organisations were to such an extent that their management services contract was left unsigned for more than three years.
"There are difficulties and niggles occurring at each level and every part of the relationship between the two organisations", the report said.
Williams' last day at council will be July 23, with Chief Resilience Officer Mike Mendonca stepping in as acting chief infrastructure officer while a recruitment process is undertaken.
McKerrow said in her email Williams had worked hard to create the future foundations for Infrastructure and delivery.
"He has overseen the process to create a consistent and integrated approach to strategic asset management, initiated the development of our Project Management Office, set in place the focused development of Te Ngākau Civic Square, built a strong working relationship with Wellington Water (and with other key contractors) and actively participated in the WCC contribution to three waters reform."