Union Gas set up a free kit for us that included some 1.25 GPM 'energy-efficient' aerators and shower heads. I took one apart to see if I could retrofit this onto the rest of our faucets, and found that these new aerators had just one extra piece - a thin disc with a small hole to restrict water flow.
All you need are the tools to remove your current aerator (I used slip-joint pliers), a type '2' plastic bottle with a flat panel (I used a Sunny D bottle), strong scissors, a 3/32" drill bit, and Teflon tape.
First, I removed the standard 2.5 GPM aerator and took out the gasket. Using that as a template, I cut out a plastic disc from the plastic bottle. The pictures are pretty bad because I couldn't get the lighting conditions right.
^ That disc was a rough first attempt. The jagged edges are fine, but make sure it will fit snugly into the aerator.
Using a 3/32" drill bit, drill a hole into the centre of the disc. Slip the disc in behind where the gasket sits, and make sure that it is snug on at least two sides (try a loose disc...very loud whistling).
Reapply Teflon tape to the aerator, reinstall, and test the water flow. I doubt the little disc presents any danger of putting BPA into the water, but if you want to be safe, don't put one on the faucets used for drinking water.
