Last month we went on a road trip looking at colleges for my son. At one
motel in San Diego they had the worst shower I can remember. It was
designed for vertically challenged people and the flow was so low that
it took a very long time for each person to take a shower.

A long time ago I used to take a shower head along when I rented ski
cabins or condos and I am going to start doing the same when I go to a
motel. Just an adjustable wrench and a modified shower head is all that
is required.

Not all shower heads lend themselves to modification. Twenty years ago
there were shower heads with removable restrictors where the
instructions advised you to be sure to replace the restrictor after
cleaning the shower head so that the water saving feature would still
function (wink, wink). Not sure if there are any of those still around.
I bought an inexpensive, solid brass shower head at Home Depot for $18.
I removed the water-restriciting rubber washer and replaced it with
normal washers http://www.homedepot.com/p/204511132. Then I
disassembled it and drilled out the water restrictor hole, increasing
the diameter by about 4x. I would not try this with a plastic shower
head and many of the shower heads sold at Home Depot, even the more
expensive ones, are plastic with a metal coating.

Apparently this is all going to get worse. In NY, they already have
reduced the GPM for showerheads to 2.0, from the federal guideline of 2.5.

I saw a shower head on Amazon that is supposed to be 4-5 GPM
http://www.amazon.com/dp/B000ZSF296 (apparently it ships with a
restricting washer in order to stay legal).

I don't get these low-flow shower heads. It just takes far longer to
take a shower and you end up using the same amount, or more, water. They
need to rate shower heads in gallons per shower, not gallons per minute.