Underground water pipe

Albe

I have many big raised beds for the veg at the end of the garden. Last year watering them with tap water costed me a fortune, and too much time. So this year I've arranged a rainwater harvesting system with IBC tanks for storage.
Now I'm making a water line to take this water to the plants.
Ideally I'd like to bury the water line underground. Here some questions:

*) many moles visiting our area, from spring to autumn. Will they damaged it?  How to protect it?
*) I'd like not having to remove it every winter. How do I make it freeze proof? My idea is to install a leak valve so in autumn flush the water out of the line. How can I do this without having to buy an expensive air compressor? Are there manual pumps to push the air through? Or cheap compressor? Or anything else?
*) what material is best suited? PVC is cheap and flexible. Copper is expensive but better resistant to rodents. 
*) How deep should I make it? Right now I digged a preliminary trench 10cm deep....


Happy watering everyone.

steephill

Moles won't damage a water pipe.

You might be overthinking this, your system won't be like a pressurised mains water supply. People leave soak hoses and dripper systems out all winter without major problems, they are naturally leaky and will drain themselves out once the supply is turned off.

Use blue MDPE water type like the water companies use for domestic supply. For those domestic supplies you need to bury it 750mm deep to avoid freezing but you will need to insulate where it comes above ground unless you drain it down.

A drain tap half way along the length in an access pit serving as the lowest point would be the easiest way to drain it down for winter but you might be able to blow it clear using a car tyre inflator or even a manual bicycle pump. It won't need much pressure to shift the contents of a pipe open to atmospheric pressure.

Albe

Thanks.
I used the word pipe but what I actually have right now is PVC flexible hose. Would this do?
Whatever I end up using, I'm happy to leave it out (buried 10cm underground) all winter provided I have confidence I manage to drain it...

Wilderbeast

Think there was a similar thread previously on these lines. You will need a decent bore pipe if it's taking the water any distance (I don't know the maths but gravity flow through a standard hose pipe is tiny). 10cm depth will not guarantee frost free at all, mind I'd simply disconnect from the tanks and use my lungs to blow the water out (works great on my 70mt of hose pipe).