Installing a permanent water line sure beats handling (and re-handling)
250' of hose.
Last time I used a ditch witch it made a really nice trench 4" wide and
18" deep. (except where it encountered a pile of rocks). It made an excellent water line trench. The ditch witch itself was a real bear to operate. First of all, it weighs around 800 lb. Don't plan on putting it into your car's trunk. It had wheels which could be driven together or separately. Steering was basically nonexistent. You had to kind of lean on the handlebars sideways to keep the thing going in the direction you wanted. To make a sharp turn, it was easier to lift the digging bar, reposition the witch and start a new trench. If you can't lift really heavy things, get a friend who can to help you run the ditch witch.
Use 1" or larger polyethylene tubing (the black stuff). It will hold up to occasional freezes. It resists UV where it sticks out of the ground. You can put a hose connection at both ends and just let the end stick out of the ground. If you want to be fancy, put a pressure treated 2x4 at the end and use some of the metal pipe clamps (you need some of them anyway to connect plumbing connectors to the PE tubing) to hold the PE tubing on. You can put a faucet at the garden end, although I recommend using a T and putting two faucets there. You can fill a bucket while a hose is watering something. Using 1" tubing will reduce the line pressure drop. Home Despot carries all that stuff.
At the house end, I just use a washing machine hose (about 4' with two female couplers) to connect the PE tubing to the hose c*ck.
At the low point in the line, install a valve box and put a drain valve there so you can let the water out for the winter. Alternatively you can buy an air compressor and blow out the line in the fall. The valve is cheaper. If there are any ball valves in the line, make sure they're open over the winter.
If you know where your fuel lines are, I would strongly advise using a shovel to dig by hand in that region. If you don't know where they are, either go as far around as you can to avoid the area or get professional help on the installation.
I used 1.25" stuff for a 700' run. The pressure drop does not appear to be more than about 10psi at 5gpm. Since the pressure starts at 40-50 psi I think I still have enough to work with. The 1.25" polyethylene tubing was a bit more expensive than the 1" stuff, but was still affordable.
1.5" is probably available at HD also. Larger than that gets pricey and you'll have to go somewhere else to find it.
If the water pressure coming from the main is significantly higher than what the sprinkling system will use, then run high-pressure along the long run, and put a regulator at the other end of it. In my area, the water pressure fluctuates between 95 and 105 PSI, so it wouldn't be a problem for me - but I realize that not everyone else is so lucky. : )
Some people don't even use a regulator on their sprinkler systems, they just hook 12 or more heads on a single circuit. With all of that flow and the restriction of 3/4" pipes, it ends up dropping the pressure enough that heads don't blow up... but the water hammer is unbelievable!
The ditch witch will do a good job if there are no significant rocks but it takes a healthy fellow to operate it.
I ran a 1" line to my garden, total run about 300 feet and have plenty of pressure to run several sprinklers at a time.
If you want a guarantee then you will have to get the specs on the sprinkler heads and know how many you will be running at a time. That will give the flow and pressure requirements at the sprinklers. Then calculate the pressure drop on your line and deduct that from the head pressure at the inlet.
If I did my system over I would install a couple of inline shutoffs and drains for when I poke a hole in the line from time to time.
If you are in a frost area you will want to drain the system. I blow mine out with the compressor.
5 gpm is a lot for a home water system. The pipes in the house are generally 1/2", although 3/4" pipe is sometimes found. Take a gallon jug and see how much time it takes to fill it from your hose c*ck. I can get around 5 gpm through mine (12 seconds/gallon). My kitchen sink will produce around 2 gpm and the bathtub will do about 4.
Take a garden sprinkler and put it in a 5 gallon bucket. My guess is that it would take significantly longer than a minute to fill the bucket. This would be a useful exercise to do anyway, since you need to know the rate if you want to control the amount of water your garden gets. A 50 x 50 garden (2500 sq. ft.) needs about 1550 gallons (US) to approximate 1" of rain. (1" over 2500 sqft = 208 cubic ft, about 7.5 gallons/cubic ft [Handbook of Chemistry and Physics, 37th ed.]). This is one reason why drip irrigation is so popular with large growers. The water can be applied to the crop, and not to the weeds between the crop. You can possibly reduce your water useage by a factor of 10.
A 50 x 50 garden could be covered by one sprinkler moved around on a regular basis. I've done it on a 75 x 100 garden, but it takes several days.
The easiest way to reduce the water pressure is to just not open the valve all the way. This isn't a precision application: a factor of two in application rate is within reason.
When I first used a ditch witch it did a great job, making a nice narrow
4" wide trench until I came to a foundation for a stone wall that had become buried over the years. Man, did that thing jump around. It actually managed to pull out the rocks (they stalled the ditch witch several times), some of which had dimensions in the 8-12" range. The resulting hole was about 2' wide at that point.
I also found a buried barn foundation. Those rocks were in the 3' range. The ditch witch didn't move them much, but they certainly moved the ditch witch around.
It takes at least two healthy fellows to operate it safely.
Where I live, everyone is on private wells. No public water. It's possible that a public water system could deliver more pressure/volume than an individual well (after all, they have to be able to supply fire hydrants).
Most people will still be limited by the size of the pipe within the home leading to the hose c*ck. 1/2" pipe is most common in older homes with 3/4 used for some of the main runs. I wouldn't know about newer homes.
I am on a private well and get plenty of water but I designed the system that way. I run a 1-inch line directly from my pump to the garden. That is easily sufficient for my needs.
I have not gone through the numbers but I am pretty sure that I can get more than 20 gpm in the garden 200 feet from the pump.
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