Leigh Kamping-Carder

Manhattan real estate has one constant, and that's change. You can tell by walking the streets or, for the data geeks among us, by checking out the 61-page survey of a decade in co-op and condo sales, released today by appraisal firm Miller Samuel and residential brokerage Douglas Elliman. We’ve slogged through it for you to find these three tips that will give you a better idea of what to watch out for in today's market.

The New York Times made quite a, ahem, splash yesterday with a lengthy investigation into the cleanliness of New York City’s domestic water tanks, finding E. coli and fecal contamination in a sizable percentage of the tanks it tested. (Yes, these are the ones that sit picturesquely atop residential building roofs across town; the newspaper estimates there are 12,000 to 17,000 of them.) So how do you find out if your water tank is safe? And if it’s not, what do you do? Here’s a quick primer.