Southern Water customers were without water for two days after a technical problem at the Testwood works prevented water from leaving the site.
The water supply company said the issue was not related to sewage, but confirmed planned works were the cause.
While starting up the site, it was noted that the water was not meeting the stringent water quality standards.
As a result, the site shut down automatically, meaning gallons of water had to be disposed of.
“The initial issue was turbidity (where it is harder to treat water) and there were secondary issues following this that involve how water is treated.”
A total of 73,000 properties in and around Southampton were affected, with 58,000 left with no water.
Thousands of people queued to collect water from bottled water stations dotted across the city.
Southern Water said it is “carefully considering” the issue of compensation and will provide further details to customers and businesses impacted in due course.
Water was totally restored in the early hours of Friday morning.
Tim McMahon, a managing director at Southern Water, acknowledged that part of the company’s response “fell short” during the outage.
He said: “We will be carrying out a root and branch review of this incident to make sure those issues are not repeated, especially in relation to our initial response of setting up bottled water stations and deliveries to customers on our Priority Services Register.”
He added: “Testwood Water Supply Work is undergoing a huge £250m investment to modernise it and ensure customers have a resilient supply in Southampton and the surrounding area.
“This has meant our teams are undertaking a huge amount of work at the site, and during this it led to some unforeseen issues that have taken time to resolve.
“We’d like to reassure customers that the site shut down as it should do when issues arise and those issues have been fixed and no water ended up in supply that was not fit for consumption. “