Rainshower heads produce more water which leads to an increased need for the right size drain so it can drain efficiently. Also, you mentioned you just remodeled a bathroom, was a tub converted to a shower? If that was the case the shower requires 2" pipe in comparison to a tub which only needs 1 1/2". so the portion of the pipe must be changed to a 2" pipe.

Jenna, keep a very careful paper/electronic trail of all your communication with the contractor. I had a contractor quit, and then later sued me saying that I fired hiim which I did not. We had a very good paper/electronic trail of all our communications proving that they quit. We prevailed in court, but we would not have if we didn't have that paper/electronic trail. If you are missing any evidence that they refused to fix, create a retro-active trail of that communication by sending an email to the contractor that says something like this: "Thank you for meeting us at the work site yesterday to discuss the poor tile placement and faulty waterproofing of the shower you built. We were really hoping that you would decide to move forward to fix the problems, but since you refused, we are now stuck in a situation where we need to hire a new contractor to re-build the shower. I would like a refund of [$$$] to cover [$$$] to re-puprchase tiles, and [$$$] to hire a new contractor to re-demo and re-build the faulty installation. Please bring a check, or mail one to [address] today." Make it *kinda *polite. Then save his response. You need a piece of the paper/electronic trail that proves that he refused to fix anything, or else he could claim that he was totally willing to fix, you were unreasonable and fired him instead. In most states you have to give the contractor a chance to fix. If they botch the fix or refuse to do anything, then you can legally fire them. That's what someone did to us, and they sued us, but we had the paper trail to show the judge that they had quit. They said it in an email plain as day and judge awarded us everything we asked for in our counter-suit. You need proof that he refused. Probably he will respond to your email in some rude way, and probably will not refute your description of him refusing to fix. That should work as proof. Sorry this has happened to you. I would post my "Goes South" story, but I have a feeling everyone is sick of it. But if you want to look it up it's called "What to do when a project goes completely SOUTH." Good luck, and take tons of photos of every layer of everything that is underneath those tiles. You may need them one day. We did.

If I were you, I'd assume that you paid for it so I'd call him and tell him you'd like it back. You can approach it with him that you want it in case you need to do any repairs. He was wrong in not asking if you wanted it disposed of or not. And the other thing is that cedar (as with all wood) right now is extremely expensive so I doubt he just threw it away. Give him a call and then hide that extra cedar when you get it so it doesn't disappear on its own.

After you fix the pressure issue, maybe with adding a separate pressure tank, then you have to fix your hot water supply issue. 7.2 gallons per minute, would mean a 10 minute shower with a typical tank. But, if you had enough pressure, you'd be blasted clean in that 10 minutes! But no one after you would have hot water available. A commercial boiler could possibly create enough volume to sustain multiple showers. That would be very challenging production for a tankless, except in the warmest areas of the country, like Florida. Incoming water temperature controls the temperature rise and flow that is possible. A series of 2 tankless, with the first acting as a preheater, might possibly work for a cold climate. But it also might not work, as they have minimum flow rates to trigger the burner. There is a lot of math to figuring out the possibilities here, and they start with your location and specific water conditions. 7 gallons down the drain is a whole other separate physical plumbing issue. That will require upsizing the drain, or multiple drains. I have not even gotten into the issue of the waste of the resources, which does violate code in many many places that have experienced water shortages. You may be surprised at how many locations in the US have experienced drought conditions and water shortages. It is only getting worse.