NASHUA – It’s the type of spring cleaning that people have a hard time swallowing.

Each year, Pennichuck Water Works flushes its pipes to push out naturally occurring substances. But this annual cleaning causes a temporary discoloring of water, a sight that makes customers think twice about gulping a glass of cold H2O.

This spring has been no different, as Pennichuck moves from section to section of the city’s water line grid.

A few Pennichuck customers recently contacted The Telegraph, wondering how long their water will look brown and if it is safe to drink.

Nashua resident Michael Maas, for instance, said he can’t bear looking at a glass of darkened tap water, and doesn’t care for Pennichuck’s response to the annual cleaning.

“Pennichuck’s answer is they are flushing the lines and you have to live with it,” Maas said.

The utility, which is in the process of being purchased by the city of Nashua, asks for customers’ patience as it winds down the two-month process.

Crews are mostly flushing out manganese, a naturally occurring substance that doesn’t cause harm when consumed with water, said Donald Ware, Pennichuck’s president of regulated water utilities. Manganese has a dark color, a taste and an odor.

Typically soluble in water, manganese solidifies when chlorine is introduced to H2O. Pennichuck chlorinates its water, so the pipes have built up a lining of manganese over the years, Ware said. Also, some older pipes are cast iron and have a “soft lining” of rust, he said.

The annual flushing pushes out the manganese and rust so that they don’t appear during the course of the year when customers are drinking water or taking a bath, Ware said.

Pennichuck can’t flush in winter because the weather is cold, Ware said. So spring is the ideal time, before warmer summer weather causes customers to use more water and the sediment starts “peeling” off with increased usage, he said.

In Nashua, Pennichuck flushes the system between 11 p.m. and 6 a.m. to minimize disrupting customers’ lives, Ware said.

If customers experience colored water after a scheduled flushing, they should run cold water for five to 10 minutes to clear their service lines, Pennichuck says on its Website. If water doesn’t change, customers should call the company.

Pennichuck recommend that customers use bottled water during flushing times. But the tap water is safe, Ware said, although he acknowledges it’s not pleasing to look at. “Would anybody drink that water? It looks pretty nasty,” he said.

Maas wonders why Pennichuck doesn’t reimburse customers for using water to test and clear their own service lines.

Ware said running water for about five minutes wouldn’t qualify customers for a refund, but if they had to run water for a longer periods of time, then Pennichuck would recompense customers.

On its Website, Pennichuck lists the dates particular neighborhoods will undergo flushing.

Nashua resident Natalie Lacireno-Paquet wrote to The Telegraph that Pennichuck didn’t announce the flushing as clearly as it could have. She got a notice in April, but it was not in “very noticeable letters.”

Lacireno-Paquet also wrote: “The water is coming out of the tap brown, is brown in the toile(t), and has turned my laundry gray.”

Maas, an engineer by trade, said he believes the flushing process is inefficient and costly to customers.

“Flushing is only dealing with the symptom, and I think they know they have to replace the mains or have them cleaned or lined…to solve the problem.”

And that’s what Pennichuck is doing, Ware said.

Pennichuck is slowly but surely either cleaning pipes or replacing them. Since the mid 1970s, Pennichuck has been slowly updating 400 miles of piping in its core system, Ware said. There is about 40 miles of water lines still in need of work, he said.

Each year, Pennichuck either replaces or cleans about three miles of pipe, Ware said. It costs $1 million to replace a mile of pipe, he added.

Flushing is expected to end this month. For a schedule of flushing in your neighborhood, go to: pennichuck.com/flushing-schedule.php

Albert McKeon can be reached at 594-5832 or amckeon@nashuatelegraph.com.