Actually what I have done on my last couple of brews is the following.
I use an immersion chiller.
With summer and the tap water being quite warm, I've been coiling the garden hose in an esky filled with water and with 2 and 3 litre juice and milk containers with frozen water in them. The hose is the inflow hose to my immersion chiller.
Basically it is not as efficient as having a copper coil in an ice bucket as the inflow to the immersion chiller but it works very well anyway.
Today I got 25 litres down to 26 degC in 28 minutes. I didn't measure the tap water but it would have been in the low to mid twenties.
for the likes of me and batz pre ice coolers are the only hope we have of cooling our wort down as our tap water is just to high to reach pitchable yeast temps this time of the year.i really like those convoluted counter flow chillers but as to there efficiency well thats anyones guess.
my money is on the ccfc though.
Here is a picture of my pre-chiller.
A small esky with the garden hose coiled in it.
Filled with water and frozen milk containers and coke bottles in there as well.
I get it ready mid boil so the water in the pre-chiller is down to single digits when I need it.