I know I can run indoor wire underground as long as it is protected in something, but can I use a water hose to run it through instead of conduit or PVC?
You can't actually use indoor wire underground. The wire or cable will get wet, will degrade, leak, and do really strange things like electrify the ground. There is nothing you can do to keep conduit dry. It will get wet.
In legit conduit, normally you use individual wires (THHN). Almost all THHN is dual-rated THWN-2 for outdoor use! Same wire - that was easy! I work in THHN/THWN-2 and I love it.
Note the two layers of insulation.
Some homeowners are super obsessed about using cable instead of wires. That's silly in (legit) conduit! However it can be direct buried. Indoor cable (NM) is indoor-only and gets wrecked fast in the outdoors, in that case you'd need outdoor-rated cable such as UF.
Barely seen: paper packing in the NM cable.
If you ever plan to sell the property, you need to do this right. Part of the home sale process is inspections. Any not-to-code work must be ripped out and replaced (pulling permits for both the demo and the replacement, so they'll know). Once you are caught, secretly removing the work won't be an option anymore.
You can't use any random pipe-like thing to run electrical cables. Well, you can, but it doesn't count as conduit. So the only thing you can run through water hose is UF or other outdoor rated direct burial cable, and the installation will be treated as direct burial.
Also when you bury it, the garden hose will collapse, so you won't be able to pull that wire out and change it, if that's what you were thinking.
Random cheap PVC also doesn't work as conduit - only the gray electrical rated stuff qualifies as conduit. Using white plumbing PVC is just a bad idea, it'll get hung up on every joint and won't make the bends.
You can also use metal conduit, it's not expensive if you shop around and buy it somewhere other than the big-box store.
There are depth requirements for how deep you bury it.
- For expensive RIGID conduit it's 6".
- For a single circuit GFCI protected, it's 12" direct burial or conduit.
- For other legit conduit, 18".
- For other direct burial (or fake conduit), 24".
In all cases that's the amount of earth above the top. Don't trench a 6" trench and put 3" RIGID into it leaving only 3" of dirt above it.
Sure, you can...but as far as whether you should then no.
I know its probably not what you're thinking of at the moment but in the future, among other problems, someone digging around in the garden and spotting a buried garden hose might not think of it holding electrical cables.
I'd recommend twin walled cable ducting, its not overly expensive and better protects both your cables and anyone who might come across them in the future. Its always better to do something properly rather than cheap.
(Also if you sell the house I'm pretty sure a surveyor would check this and not be overly positive about your choice).