Nearly a year ago, I scribbled “Replace Brita filter” on my to-do list. But the errand perpetually fell by the wayside. There were so many more pressing tasks to complete.

“Oh, it’s fine,” I thought. “How bad can it be?” Let’s just say that a day into reporting this story, I ran out to the market and bought a three-pack. We reach for our water taps more than almost any other object in our homes — to brush our teeth, wash our faces, make coffee or tea in the morning.

To cook meals, rinse dishes and wipe countertops. To water the plants, do laundry and fill our pets’ bowls. To shower and shave.

And most often for a drink. But how much do you really know about what’s in your tap water? And if you filter it, are you using the right technology? Many of us may not be fully aware of where our water even comes from. That’s because the water that flows into our homes in the L.

A. area can be surprisingly different, ZIP Code to ZIP Code. The level of arsenic found in Compton’s tap water may differ wildly from that found in Glendale.

Malibu’s tap water may have more hexavalent chromium while Pasadena’s doesn’t have any. One tap does not fit all. “Where you are, the location, it really makes a difference in your water quality,” said Tasha Stoiber, a senior scientist at the Environmental Working Group, a nonprofit research and advocacy group focusing on environmental health.

We went to the source, so to speak — experts in the realms of science, academi.