How to dig a drain under a path or road

Here’s how to put a drain to your garden and to get the drain below an existing path or other paved area.


This is a simple, easy-to-do way of getting water to your garden when a masonry or other hard surface is between your garden and your source of water.

We might sum up this method as, “digging with water”.

What’s not discussed here are safety issues which you’ll need to also resolve such as:  are there any electrical, gas or other services where you wish to put your drain?

It’s useful for pipes between 30 to 100 mm diameter.

You’ll need:

  • polypipe or other piping to suit the amount of water and the length you wish to drive your tunnel.  For a typical household downpipe, for example, where the downpipe is about 70 to 90 mm, you’ll need the same or similar diameter pipe and the bits to join the pipe to the downpipe;
  • if the length of the path is more than a metre you may need several lengths of pipe and bits to join the pipe as it’s fed below the path and across to the other side of it;
  • a hose with good water pressure – mains water at least ie 120 kpa; the hose will need to be at least half as smaller in diameter than the pipe as the hose must fit inside the pipe and the remaining space must allow for soil to escape backwards past the hose.
  • a shovel and pick


Step 1:  dig the hole beside the starting point for your tunnel – allow about 150 depth below the base of the slab or path and make the hole about 1.00 diameter – it will have to hold removed soil and allow you to dig that removed soil out as you go further under the path


Step 2: dig a hole on the other side where you wish the new pipe to end up, about 300 wide and about 150 deeper than the underside of the slab below the path or paved area


Step 3: put the pipe to go under the path against the soil below the path


Step 4: put the hose into the pipe and turn on the water


Step 5: as the hose washes away the soil and it spills back into the hole remove the soil and place it on a pile for reuse in your garden


Step 6: continue to water pressure away the soil and gradually move the pipe further into the soil until it reaches the waiting hole on the other side of the path slab


Possible other step: if your pipe needs to be joined you’ll need to join it then extend the pipe under the path and continue your ‘water drilling’.


Go you good tunneller. Go, too, the garden to be watered with your rainwater that’s fallen on a roof nearby . . . yes?



Note: my thanks to Tim of ecoburbia whose ideas this was.



2 Responses to “How to dig a drain under a path or road”
  1. Michael says:

    Yes, it will work in tough soils; be sure to concentrate the hose water to finest point and get highest pressure; you may find a mix of water digging and poking with an iron bar will be needed; let me know how you go, please; michael

  2. Margaret says:

    Does this method work in a heavy compacted clay over shale?

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  • Michael Mobbs

    Michael is a former Environmental Lawyer who is uniquely placed to consult in four main areas:

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