Mathur was a Wharton student who had taken social entrepreneurship courses.
They thought about the one billion people worldwide without access to clean drinking water.
They thought about the high use of bottled water in the United States, despite the easy access that most have to perfectly good tap water.
By 4 a.m., they knew what they would do.
They would manufacture a reusable, filtering water bottle - a more sustainable alternative to single-use bottles. And they would use the proceeds to bring clean drinking water to areas that don't have it.
"We looked at each other and said, 'You know what, this has serious potential,' " Parekh recalled.
Sure enough, everything began to click. They were semifinalists in the computer-maker's competition. They got accepted into a Penn business-incubator program.
The job market didn't look so hot anyway, so they formed their own company, Hydros Bottle L.L.C., and waded in.
Half a world away, Winston Ibrahim was visiting a university in Israel with a strong entrepreneurship program. The Philadelphia investment banker and 2009 graduate of Johns Hopkins University was impressed with the kinds of projects those students were doing. "That kind of planted a bug," he said.
Back home three weeks later, he bumped into Parekh and Mathur. Not long afterward, the Ibrahim Family Foundation, begun by his father - S.A. Ibrahim, CEO of Radian Group Inc., a global credit risk management company in Philadelphia - provided seed money.
The first bottle, which began as a sketch on the back of a piece of paper, came out early in 2010. Bottles were in Whole Foods by that July.
A newer version - with a side fill, straw attachment, and carrying loop - is due next month.
The components are manufactured in Illinois, northern New Jersey, and good old Northeast Philadelphia.
The carbon filter reduces chlorine and chloramines - both disinfectants that many find have an unpleasant taste or odor - and particulates.
The drinking parts are covered with an anti-microbial surface, and it's dishwasher safe.
Unlike some early reusable bottles, these don't contain bisphenol A or phthalates, compounds that are thought to disrupt the hormone system.
Other filtering water bottles exist, but the Hydros guys say theirs is unique in one small but significant way: You don't have to squeeze it to get the water out.
Water in single-use bottles may be convenient, as indicated by a consumption leap from 16.7 gallons per capita in 2000 to 28.3 gallons in 2010.
It's good for disaster responses. Some say they prefer the taste. Or the cachet of bottled water from exotic locales.
And the environmental footprint has improved. The bottle-recycling rate has doubled over the last half-decade to 31 percent (although millions of them still wind up in landfills and as floating particles in the ocean).
The amount of plastic used for each bottle has been reduced by a third. Manufacturers are introducing plant-based plastics.
But to many, bottled water is still the Hummer of beverages.
Tremendous amounts of energy are used to collect the water, run the plant, make the bottle, ship it to the store, and keep it cold. The Pacific Institute, a nonprofit research and policy group based in Oakland, Calif., recently concluded that the amount of energy used was equal to what would be needed to fill a plastic water bottle a quarter full of oil.
"It's not viable for sustained growth," Ibrahim said. "We think there are better ways."
Reusable bottles - with or without filters - are certainly gaining traction.
They're a common giveaway for eco-oriented events and companies. Many people almost seem to carry them as a political statement.
About 300 colleges have installed special drinking fountains - Immaculata University has "hydration stations" - for easy bottle refilling.
"We're driving people to use a neglected infrastructure," said Ibrahim - the city water tap.
The Hydros bottle and enough filters for a year cost about $50, although the company is hoping to come up with a less expensive version for stores such as Target.
For every bottle sold, $1 goes to drinking-water projects in the developing world.
Their website, www.hydrosbottle.com, tries to personalize the venture. The thinking is that many people give to cancer research, for example, because they know someone with the disease. But how many Americans have an intimate connection with someone lacking access to water?
So for one of their projects, at a village in Cameroon called Gundom, they describe the town - its 300 residents, the cassava and plantains they grow, the language they speak, called Meta. Also: how the average household spends 52 minutes a day getting drinking water.
For $4,885, Hydros and its partners installed pipes from nearby springs and a storage system.
The idea is that communities have to want the water, not be told that they need it. And the system has to be simple enough for the village mason, say, to make repairs. It must be designed to last 30 years and not deplete local water supplies.
"For us, that means you've got economic sustainability, environmental sustainability, and social sustainability," said Parekh.
It turns out that Penn is a nexus of water activity.
Also on campus is the Philadelphia Global Water Initiative, which too seeks to bring water to people who don't have it.
Its president, Stanley Laskowski, praised the Hydros bottle and its social component. "The global water crisis requires a multipronged effort," he said, "and the idea of using an innovation here at home and using the proceeds to help in developing countries is to be applauded."
At Penn this year, all new students got a Hydros.
"GreenSpace" appears every other week, alternating with Art Carey's "Well Being" column. Contact staff writer Sandy Bauers at 215-854-5147, firstname.lastname@example.org, or @sbauers on Twitter. Visit her blog at philly.com/greenspace