I use a standard 50' copper immersion chiller, plus a cheap fountain pump from Harbor Freight (I use
this 264 GPH one, not bad for $15). Several 5 gallon buckets (cheap HD homer buckets are fine) come in super handy, but anything that will hold water can be pressed into service.
Fill a bucket with water and get it up at least level with the height of the brew pot. Be sure you can lift another bucket high enough to refill that bucket as needed. Throw in the pond pump and connect it to your immersion chiller input.
(note: technically you could use a gravity feed / siphon for this first part, but you'll need a pump for the second, recirculating, step)
Capture the first 10 gallons (refill that high bucket as needed) of hot water from the output hose into other buckets for later reuse: cleaning, watering plants, etc. That should get you under 100 degrees.
Once you reach 100 degrees, all you need is the one bucket, add ice and/or frozen water bottles, and put the output hose into the same bucket as the pump for a recirculating system, so that's the last of the water that you'll use, and can bring you down to whatever temp you need, depending on how much ice you use. (I find a 10 lb bag of ice plus several 2l frozen bottles is more than I need.) There little point to adding ice while the wort is still very hot, so save it for when it's needed.
Total water use approx 15 gallons, all of which can be reused for watering plants, cleaning brew gear, cleaning your car, washing clothes, etc.
Considering a California-spec showerhead uses 2.5 gal/min, that's the equivalent of one 6 minute shower. (or one 5 minute shower plus 1 minute to let the water heat up) Skip a shower for one day (assuming your body chemistry permits!), and it's net zero water use. Or less than zero if you're able to re-use that water in ways you would have needed fresh water for, otherwise.