Arlington is investing in its water management systems to replace aging pipes — some of which are 87 years old — and keep pace with development.

The Board unanimously approved master plans on stormwater and water distribution on Saturday, which aim to maintain a clean water supply and reduce the risk of flooding.

“Arlington is committed to providing safe and reliable drinking water to our residents and ensuring that our community complies with environmental law and remains sustainable,” Arlington County Board Chair Jay Fisette said in a statement. “These plans will allow us to meet the demands of projected population growth and help restore the health of the Chesapeake Bay.”

About a third of the storm sewer system in the county needs additional capacity to reduce flooding risks, according to the county’s assessment. And a total of 11 miles of aging steel and terra cotta storm sewer pipes — some 87 years old — need to be replaced.

The average age of the county’s water mains is 55 years, Water, Sewer and Street Bureau Chief Harry Wang said earlier this year. Between Jan. 8 and Feb. 20 alone, the county had to perform 89 repairs on water mains — and average of 2.1 breaks per day, Wang said.

The approved plan estimates the capital cost per year for stormwater-related projects to increase from $2 million per year to $3.3 million per year, depending on what external regulations require.

Home construction is responsible for a spike in the amount of surfaces like streets, rooftops and sidewalks that can’t absorb runoff, the report said. “Single-family home projects accounted for the majority of pollutant load increases from development activity in the county during the time period studied [from July 2009 to July 2013],” the document said.