The aerator screws onto the tip of the faucet, determining the maximum flow rate. Aerators are inexpensive.
The EPA reports that showering accounts for about 17 percent of residential indoor water use. High-efficiency shower fixtures cost $10 to $20 can save 25-60 percent. Older models before 1992 are the worst offenders.
Currently, the city of Norman has a low-cost kit of water efficient fixtures available at the Utilities billing office for $6. The kit contains a aerators for kitchen and bathroom sinks, a shower head, and a toilet water displacer.