The big flush: Why a river of water will be flowing down your street

They snake across our region right under our feet, just below the sidewalks and roadways and through green spaces. We hardly give them a second thought.

But the thousands of kilometres of water mains throughout the capital region feed our taps that flush our toilets, clean our clothes and bodies and quench our thirst.

Twice a year, this massive network of iron and plastic pipes need a good scrubbing.

And it’s done with a highly co-ordinated system of high-pressure flushing using the fire hydrants in your neighbourhood.

The Capital Regional District is responsible for pumping the water out of the Sooke Lake Reservoir, screening and treating it before sending it tumbling down massive trunk lines, where they reach key connection points in each of our communities.

From there, it’s up to municipalities — and in some places the CRD — to keep the pipes clean.

It’s done twice a year and in Saanich, where there are 550 kilometres of water mains and more than 47,000 residential, commercial and institutional customers, it has been underway since the new year.

In Victoria, which owns the pipe within its borders as well as in Esquimalt, flushing starts on Tuesday through about

335 kilometres of water mains and continues to May.

The region’s two largest municipalities will do it all over again in the fall.

Saanich spokeswoman Kelsie MacLeod said the high-pressure flushing ensures good water quality by removing sediment and minerals that slip through screenings and build up in the pipes, along with microfilms on pipe walls.

“If we didn’t do this, eventually sediment could build up inside the piping system and potentially cause water ­discoloration as well as taste and odour complaints,” she said.

Flushing sediments out of the piping system also helps to improve and maintain the chlorine residual in the water system, MacLeod said. The chlorine residual in drinking water is there to combat bacteria, keeping the water potable and safe to drink.

City and municipal crews use a process called “unidirectional flushing” to clean the water mains, which involves using fire hydrants to push high-velocity water through the mains.

Crews close and reopen isolation valves to direct water flow in a single direction through the water main to increase velocity so that water flows down the entire pipe to provide a scouring action.

A de-chlorinating agent is also used while flushing to ensure the chlorine residual is removed from the water before it is discharged out from the hydrants and into storm drains.

Jas Paul, assistant director of public works for the City of ­Victoria, likens the process to hosing down your driveway.

“You don’t just walk on and start spraying everywhere, otherwise you’re just moving the sediment around. You start at the top and move down,” he said. With water mains, areas are isolated and cleaned out before moving to the next area.

Paul said the flushing is a “highly co-ordinated event” with rotating starting points each season. Crews are usually sent to neighbourhoods where they do a block-by-block flushing.

“It’s one of the most important maintenance tasks that a public works department undertakes,” said Paul. “It’s not only essential for maintaining water quality and [public health], but it also tests the overall effectiveness of our water system.”

It also serves as a test of the city’s 1,800 fire hydrants, he said, “because we don’t want any problems with those if there is a fire.”

Victoria uses computer modelling to simulate the flow required to achieve the best cleansing effect in its water lines.

Pipes are also inspected to keep an inventory of what pieces have to be replaced and when, said Paul.

Many sections are being replaced each year, he said, based on risk assessments that include the integrity of pipes (breaks or leaks), corrosion, soil conditions, demand for water in certain areas and construction timing, such as when a road needs paving.

Some pipes in Victoria date back more than 100 years and are cast iron, with many concentrated in the downtown core. Some are holding up well, said Paul, but the goal is to eventually replace them all with PVC pipe, which is flexible in an earthquake and more resistant to corrosion.

Paul noted that despite population growth, particularly in the downtown core with the increase in high-rise condos, Victorians have been using less water on a per capita basis over the past 20 years.

He credits a drop in outdoor watering, more efficient washing machines and low-flow toilets. “[That] allows us to save millions in not having to upsize pipes,” Paul said.

During water-main flushing, residences and businesses can see some water discoloration or low water pressure when they turn on their taps. It’s temporary and not a health hazard, according to the CRD.

The CRD’s Integrated Water Services Division does flushing for Sooke, East Sooke, Colwood, View Royal, Metchosin and Langford every year.

It will start in various areas of ­Langford and Colwood between Feb. 1 and May 28.

Central Saanich, North Saanich, Oak Bay and Sidney do their own flushing programs.

Residents can check with their area for schedules.

Commercial establishments such as laundromats, beauty salons, breweries, hotels and restaurants can check with public works departments for advanced warnings of flushing in their locations.

dkloster@timescolonist.com