My practice, since 1993, has been to place 4 gals of water in a freezer for 3-5 hours prior to brewing.
The water I use is tap, but it is filtered through a PUR water filter (the kind that screws on to the faucet).
I boil 1.5 - 2 gals. I usually lose about 1/5 gal in the boil and when transferring between the primary and secondary.
I place a nylon net on the primary prior to pouring 2 gals of cold water in. then I pour in the wort. The net aerates the wort for me as well as catches the hops and Irish Moss, etc. Then I sparge the contents of the net with another gal of water or so. Afterwards, I squeeze the water out of the net and remove it to the sink, then top off to 5.5 gals.
I'll stir this for several minutes to mix it pretty well. I take a sample with a thief and place it (the sample) in the plastic tube to take my temp and hydrometer readings.
Usually my temp is in the 70s (within minutes) as soon as I bring the water level up to 5.5 gals. Then I'll pitch the yeast, place the lid on and an airlock and move to its happy fermenting place....
The process is pretty simple and it works for me.
Now when I use grains the instructions change a bit, but everyone knows that.