Hi GTN, Very good question. I'll bet your 3/4" spigot has a 1/2" copper line feeding it nor is a spigot 3/4" through out it's length. Smaller to bigger or vice versa doesn't matter. Size affects velocity at that change point, but very briefly. Length of pipe is what affects the system efficiency (loss of pressure) the most. Water flows faster through the smaller diameter pipe and when water velocity gets high enough turbulence in the pipe is reached and your friction loss per foot of pipe increases as well as noise. This friction loss robs you of pressure as the water travel along the system. Your system has high pressure so this not a big concern in your system. It becomes a design issue depending on where you reduce your pressure for your garden. 1 1/4" pipe was sized by a formula that calculates flow versus velocities in various size pipe. A standard design criteria for non-turbulent flow is less than 5 feet per second velocity(noise reduction). Using that criteria the 1 1/4" was acceptable, 3/4" would be less acceptable but still can be utilized with no real problems. It then becomes a cost issue. It makes no difference what size the source pipe is, but hooking up to your house affects the velocity of water traveling through your house pipes. If you turn on your hose, how noisy is the flow in your house? Does it affect the flow of other water using appliances being used at the same time? Turn on the washer, shower, kitchen faucet, etc an listen to the sounds of the water. If the answer is no to these questions your house water system doesn't pose a constriction to your garden water needs. The more items being run the noisier it gets. Did you ever call your builder and find out about the pressure regulator needed for your house water system? Just curious. GL. Aloha

the solenoids need to be turned clockwise till they are snug and any bleed screws need to be closed. if that doesn't take care of it you may have some cross-connected wires.

A single 55 Gal watering system can be done between $100 - $200! (excluding pump)! Where as we collect water into a 1200 gallon underground tank and use a shallow well jet pump for distribution to our five water stations. Initial installation costs were over $4,000 in material and I did the work! And I'm considering adding an additional 800-1200 gallon tank! Your issues are going to be 1. What do your local building codes allow. 2. How large a tank can you use. 3. A large $$$ for you is going to be the size of the pump needed to pump water to the roof! Hope this helps........

600 feet is nothing, 20 gpm is good flow. We have a well that was put in for automatic animal watering troughs that runs at 5 gpm that we dont have an issue with (yet!). The 1" mainline should suffice, as you will lose pressure due to friction in a smaller diameter. Run the PVC to the garden, then connect to 1/2" poly tubing or layflat for a submain and run your drip tape off of that. They sell pressure gauges that you can attach to the end of your lines to check your pressure. I would definitely go that route before buying a pump. You will need to regulate the pressure downward when going from the PVC -> submain line. Props on working towards becoming a full time farmer. I started last year and I am broke as a joke but wouldn't trade it for any job with a boss or a timecard!