I'm in neighboring Howard County.. I sincerely doubt there is anything in your water that is causing algae.. That said, it would help to identify what you have first. Take a look at the sticky post in the algae forum, and see if some of the algae guides can help out.
Montgomery takes raw water from the Potomac and Patuxent river rivers, then filters, disinfects, fluoridates, and pH adjusts it.
Howard buys from Baltimore county, which basically does the same thing using reservoirs.
Municipal water reports generally don't help much, but MoCo's can be found here:
Consumer Confidence Reports for Montgomery County, Maryland
Unfortunately they generally don't care about the same parameters, they're mostly monitoring toxins, etc. You could call them up and ask if they've changed anything recently, but I doubt they have.
About the only thing I've noticed is that periods of high rain tend to drive down GH and KH, while drought drives these parameters up. The utilities don't generally monitor GH, calcium or magnesium, and also generally don't monitor alkalinity. They for the most part monitor pH to keep the water from being corrosive to pipes, and that's about it.
none of the waters in Maryland are terribly prone to silicate, which can spur diatoms. Pretty much every other algae that afflicts us is more stimulated by what is missing from the water than by what is added to it, assuming the water is good enough to grow plants in at all.
BGA, actually cyanobacteria, isn't really an algae, but seems to be spurred by low nitrates... Unlike plants, many cyanobacteria can fix nitrogen from nitrogen in the air, thus are likely to thrive when plants are suffering from low nitrate.
Pretty much every other algae that exists needs exact same nutrients as your plants do, because they are also plants... There's nothing "extra" that will foster their growth that your plants don't also require.. That said, algae are simpler life forms than high-order plants, and generally can deal with deficiencies better than plants.
I'd also look at your light vs CO2 balance, as many algae like to take hold when there's too much light, and take advantage of low CO2 levels that plants often can't use. Usually BBA and its relatives crop up under these conditions.