The basic gist is this: the average showerhead and sink aerator is set to a fairly high gallons-per-minute, or GPM, rate because energy used to be cheap and the ideal was to cover yourself (and/or your dishes) in as much hot water as possible while cleaning. Think those rain shower things. Which is all well and good if you don't care about the cost of the water and the cost to heat that water, and then overall world conservation problems regarding water and energy resources.
But I care, because I hate paying more for bills than I have to, and I live in Vermont, and climate change and world resources and all that stuff is a Big Deal here. I mean, we're going to mandatory composting of household food waste in 2016, so.
Previously, I had already done our showerheads, which was an easy thing to do. Last weekend, I tackled the three sinks in the house: kitchen and two bathrooms. Some of the aerators didn't have info on them but the one I removed from the upstairs bathroom was marked as 2GPM. I replaced it with a 0.5GPM aerator, so I cut both water use and energy use in 1/4 by replacing it!
Here's the step by step of the process. I used these aerators from Niagara; they cost about $1 apiece, which seems insanely inexpensive to me! They should pay themselves off very quickly.
Step 1: the old faucet in our upstairs bathroom sink
Step 2: here's what 2GPM looks like
Step 3: wrap the old aerator in an elastic. this will provide better purchase for the wrench and make sure it doesn't scratch the metal
Step 4: remove the old aerator simply by turning left with a wrench or pliers
Step 5: here's what an aerator-less faucet looks like. clean out the faucet a bit, there's probably mineral buildup in there. you can soak it with vinegar if your faucet is shaped correctly, or just take a small brush up in there, or just loosen it with your fingers
Step 6: here's why aerators are a thing! water goes everywhere without one
Step 7: place the new aerator in and get it threaded on. my least favorite part; for some reason I've been having horrible trouble threading things lately
Step 8: elastic again!
Step 9: tighten as much as you can. don't half-ass this, or water will go everywhere
Step 10: here's what 0.5GPM looks like!
Step 11: voila! a bit deeper than the old one, but by maybe only 1/4"