Why not gray water?
 

Thinking this morning why not have a large tank, 1,000 gallon or more filled with shower water only? Aside from a separate pipe I would see now real drawbacks. The more you shower the more heat into the system. If done right you could plumb the tank to circulate the water in it also. Maybe add in the washing machine if you need more heat in the tank. Or would a small amount of bleach hurt the heat exchanger? Maybe sink a couple of car radiators and make a closed system for the heat pump in the water tank.

I don't know, it just sounds so dumb to use cold ground water when you could use the same water after you paid to heat it up...now I have to pay to get rid of it also? Why not get my heat I paid to put into the water back out, before it goes down the drain, so to speak?

Seems like a larger family would really benefit from this way also? No drilling, no digging in the yard.

There was some talk here a while ago about waste water heat recovery. Check out these threads:
Drain water heat recovery
DIY Grey Water Heat Recycling...

And here is a nice experiment:
The Amazing Heat Scavenger Experiment

That study show some pretty promising results!

Adam

I used to just plug the drain when I took the shower and then let the water go down once it was close to room temperature. It added extra heat to the house, no question, but it added more moisture to the house than I was comfortable with(infiltration/exfiltration dew point concerns) so I stopped doing it outside of when the house was dry enough to consider it. I also didn't like cleaning all the soap scum out and now I've got my showers so short to where there's very little going to waste anyway.

Same here..I use to let the water sit in there and then I had to clean it/and all the moisture was requiring me to just run my vent more.

Depending on where its located, maybe hook the drain up so that is flows through a series of metal pipes laid under a floor (20ft?) before it goes down the drain. I bet it would give up most of its heat if the run was long enough? Probably have to insulate it from below.

I wouldn't use a big tank. I could only imagine what that thing would look like inside after a year of showering...hair, scum, grim, dirt, sand... I'd think you'd have to clean it often or else it would start to really stink on you.

A friend of mine built a drainwater based HP many years ago. I think it ran for 10 years then he got bored and designed something else. It was 6kw, IIRC.

It's currently costing me $2.75 per month to heat water for 3 people, sure you can draw more heat out of it so the grey water is colder then the incoming cold fresh water, but that $2.75 in natural gas is pretty cheap, it's less then a days worth of heating the whole house on a cold day.