Most <1" thick hardware store foam pipe insulation is about R5 or less, but newer thicker foam pipe insulation is becoming more common since many places (at least here in the PNW) now require 2" thick R10 pipe insulation (Energy Star style).
At a minimum, cover all hot water pipes you can access, using pre-fab corners or careful 45º miters at turns. Taping joints is pretty optional, but is optimal. Also insulate the first few feet of cold supply pipe at the water heater, if you have a tank style. The cold water pipes near the heater can also loose heat.
Try local big box stores if you have nothing else, otherwise try local hardware stores and builders' lumber and supply houses. The builders' supply places often have better quality stuff, at slightly higher prices, because builders don't want to hassle with cheap crap that homeowners are often willing to use to save a few bucks.
If you're more concerned about water waste than energy waste, a hot water circulation pump might work well for you. It circulates the hot water to a specific fixture (say the kitchen sink) so that the hot water is ready to go. You can also do this by installing a smart water heater under the sink that provides hot water until the water coming into the under-sink heater is hot. The circ. pump can be motion activated or on a timer depending on how you need it to work.
Hope this helps.
