Water main breaks are such a common occurrence near Paola Casale's coffee boutique in Roxboro that some of her customers call ahead to make sure they won't encounter any traffic headaches on their way to her shop.

"They ask me if it happened again. Yes, again," said Casale, the owner of Tazza di Mattina on Commercial Centre Street. "We're known for that. There's always something in the area."

The shop is just south of Gouin Boulevard near 2nd Avenue — one of Montreal's worst spots for broken pipes, a CBC analysis of 16,000 water main breaks reveals.

Since 2000, at least 50 breaks had to be repaired in Casale's area.

Although pipe breaks are a frequent occurrence all over the city, Montrealers in some neighbourhoods have to contend with far more leaks and gushers than others, as well as the resulting inconvenience.

The map below gives a general view of the hot spots — the places where breaks happened more often than average — and where they happened least. Data is only available for the City of Montreal and not for the demerged suburbs.

(Darcy Hunter/CBC)

Montreal has invested vast amounts of money in upgrading its water infrastructure in recent years, and it shows: fewer pipes are breaking.

With help from the federal and provincial governments, the former Denis Coderre administration nearly tripled the money for pipe upgrades, from $93 million to $261 million over three years.

The Valérie Plante administration announced a program earlier this month to better train blue-collar workers to fix pipes more efficiently, and pumped more money into water-related infrastructure in its first budget.

There's a lot of work to be done. About 13 per cent of more than 3,600 kilometres of pipes are in urgent need of repair or replacement, the city said last year, leading to the loss of millions of litres of treated water due to leaks each day.

According to this website that tracks the city's performance, pipes should last between 80 and 120 years. Montreal's pipes are, on average, 61 years old — older than other large Canadian cities.

Report card, by borough

Ville-Marie and the Plateau-Mont-Royal are among the city's oldest neighbourhoods, so not surprisingly, with their aging water networks and dense population, they recorded the highest number of water main breaks in the city.

Over 18 years, the Plateau has succeeded in dramatically cutting the number of breaks from 151 in 2001 to just over 40 in 2016.

Ville-Marie's record, by contrast, is the opposite: the downtown borough had 48 breaks in 2000 and peaked at 116 in 2014. In the last three years the borough has shown some improvement.

When boroughs are compared by the number of breaks per kilometre of pipe, the Plateau Mont-Royal leads the way with the highest number of breaks. It's recorded 1,136 breaks since 2000 over 168 kilometres of pipes: that's 6.8 breaks per kilometre.

The boroughs of Montreal North and Pierrefonds-Roxboro follow close behind.

Ville-Marie has the seventh highest score, with 4.1 breaks per kilometre.

The City of Montreal did not provide explanations for these problem areas, nor why some boroughs, such as Outremont, have such a stellar record. City spokesperson Marilyne Laroche Corbeil said the city looks at the water network as a whole.

"The breaks are caused by a combination of factors," Laroche Corbeil said in an emailed statement. "Our analyses are made for the entire territory, not by sector. It's impossible to interpret the data rigorously by sector."

Nonetheless, here is a detailed look at some of the problematic areas, along with explanations, if available.

Pierrefonds-Roxboro: perennial hotspot

Pierrefonds-Roxboro has recorded a high number of water main breaks for years, but that peaked in the early 2000s. There were more than 200 breaks in 2004 alone, mostly concentrated in the eastern Roxboro area.

The borough says that neighbourhood has some of the oldest pipes, but the borough also installed poor quality cast-iron pipes in the 1990s, and these are more vulnerable.

"Some old cast-iron pipes do not have interior concrete protection to meet current standards. As a result, they are more fragile to temperature changes," said borough spokesperson Johanne Palladini.

Lachine: huge improvements

Lachine had a lot of water main breaks between 2000 and 2003 (in one of those years, 103), but its record has improved dramatically since.

Notice the concentration of light dots on the map below, showing older breaks, and relatively fewer darker, more recent ones.

Saint-Michel: environmental complex a problem area

One of the city's biggest problem areas is around the St. Michel environmental complex, which was the Miron quarry until the late 1970s and the city's main landfill site for decades, until its transformation into an ambitious environmental rehabilitation project.

Neither the borough of Villeray–St-Michel–Parc-Extension nor the city could explain why so many breaks happen here.

Why do so many pipes break?

Water main breaks are a hassle for residents and for motorists, and they're costly to fix. They can also pose a health hazard, since they're an integral part of the drinking water network. Often, a break triggers a boil water advisory, to prevent water-borne illnesses.

There are many reasons why pipes break, according to Ronald Gehr, an associate professor of civil engineering at McGill University.

Gehr lists five main factors:

age of pipes.

pipe material.

soil conditions.

freezing water.

the "water hammer" effect caused by sudden valve closure.

Iron pipes without anti-corrosion additives can wear out quickly, and concrete pipes are susceptible to salt corrosion, he said.

Montreal's clay-heavy soil doesn't help, said Gehr. Clay expands when wet, and a leaking pipe can cause the soil to shift, breaking the pipe. Rocks in the soil can also break pipes.

"Heavy traffic loads could move stones near the pipe and damage it," he said.

Methodology

Data on water main breaks came from the City of Montreal's open data portal. Although the data goes back to the 1970s, much of it is inconsistent and unreliable before the year 2000.

Analysis was done using geospatial software from Esri.

The locations of the breaks were run through the Optimized Hotspot Analysis tool in ArcMap, which uses the Getis-Ord Gi* statistic to find zones with more events than the overall average.