The way Mike Oakley explains it, Ventura's new water treatment plant is like a maximum security prison for harmful bacteria and pathogens.

Instead of armed guards and reinforced concrete walls, however, the water facility relies on a filtration process that stops even the tiniest microorganisms from flowing into residents' tap water.

"There are no bacteria that can slide through this stuff," Oakley, a veteran water plant treatment supervisor, said of the filtration system's microscopic pores. "Simply put, it gives us full confidence that nothing is sneaking through."

Costing more than $22 million, the Avenue Water Treatment Plant is the most expensive and complex capital improvement project in city history, officials said. It replaces an existing, 75-year-old water plant that has been decommissioned but will remain on site.

More than 100 people gathered Wednesday inside the new plant off North Ventura Avenue for a formal dedication, lunch and tours. The ceremony included the unveiling of the water plant's new public art piece: an 8,000-pound galvanized steel gate at the main entrance.

Artist Paul Hobson said he created the steel, rolling gate as a tribute to the heroic machinery of technology and to the art deco murals and bas-reliefs created during the Work Projects Administration from 1935-43.

The new plant, one of three in the city, can treat up to 10 million gallons of water a day. It will provide cleaner, more secure and more efficiently produced drinking water to roughly half of the city's 31,000 households, said Councilman Neal Andrews, the city's representative on the Association of Water Agencies of Ventura County.

Perhaps more important, Andrews said, the plant could someday be expanded to 15 million gallons per day and be further modernized to meet ever-evolving and increasingly stringent water regulations.

Asked how long the treatment plant could be expected to operate before it becomes antiquated, Jim Passanisi, Ventura's water superintendent, said "probably 100 years," adding that every motorized device in the facility is monitored by a computer.

The centerpiece of the plant is its "ZeeWeed 1000" membrane filtration system, developed by Zenon Environmental Inc. of Ontario, Canada.

Pretreated groundwater is drawn through thousands of membrane fibers that have a pore size of .02 microns, far smaller than harmful particles like giardia and cryptosporidium, which can cause illness, Passanisi said.

"The pores provide a direct and consistent barrier" to these contaminants, resulting in cleaner water, he said.

As for taste, however, customers probably won't notice a difference, Passanisi said, adding that some people like the taste of Ventura's water while others revile it. "We are focused on water safety," he said.

Although the plant still relies heavily on an experienced team to monitor the process and conduct daily water tests, the fully automated system over time is expected to use less electricity and chemicals, Oakley said. Water treated at the plant comes from wells next to the Ventura River at Foster Park, he said.

Also attending Wednesday was Mike Ali, a senior sanitary engineer with the state Department of Public Health's Drinking Water Program, which regulates municipal water systems. He said the benefits of Ventura's membrane filtration system include ease of operation, low chemical usage and the ability to handle water quality that changes rapidly, especially during heavy storms.

"This is a state-of-the art facility, no doubt," Ali said.

Bill Hicks, a Casitas Municipal Water District board member, agreed. "Other cities and water officials will be coming here to go to school on how this kind of system works," he said. Casitas provides Ventura with some of its water, and a handful of other water agencies also were represented at Wednesday's event.

Some of the $22 million construction cost was financed through a low-interest loan from the California Drinking Water State Revolving Fund program, Mayor Carl Morehouse said. The construction was completed under budget and ahead of schedule, he said.

Design, engineering and project management likely cost an additional $10 million, Passanisi said.