I am going to go with the adhesive lined heatshrink - two ot three layers.

All I know is deep well submersible pumps on mains voltages work with the hot melt heat shrink tube. That is what came in the box with my well pump.

 

need to join a two conductor cable - 12V, 1A. The join will be submersed in 1m of rainwater.
I need a reliable way of doing this, please.

Sorry, the last post I read was...

It is 3A mains cable

And didn't realize it was the type of wire used.

 

I have done a waterproof splice with rather unorthodox materials, and it has lasted five years so far. It was in a desperate situation in a campground ten miles past nowhere late in the evening. A 3-conductor extension cord. I staggered the three joints an inch apart and twisted the strands together tightly. Then I brushed on multiple coats of PVC plastic pipe cement, the clear stuff that dries quickly. I overlapped the ends of the outer orange insulation a bit and brushed on a lot of that cement.It survived rain and being in a puddle. That was a 120 volts cord, no problems. It should work for12 volts as well, but I suggest soldering the splices without any stray strands poking out..
The really cool part is that the stuff is clear so it is easy to examine the splice.

 

When my father sold submersible pumps, he always kept a can of 3M™ Scotchkote™ handy. It is rather expensive, but very reliable for submersed electrical connections.
Try searching for "heat shrink tubing with sealant". These add something akin to hot glue to seal the ends of the joint after shrinking.

+1 for Scotchkote.
https://www.3m.com/3M/en_US/p/d/b40046251/

https://forum.allaboutcircuits.com/...imp-connector-its-criminal.121925/post-977928

https://forum.allaboutcircuits.com/...ioshack-vu-190-tv-antenna.161631/post-1414588

 

Never used Scotchkote. Is it a liquid rubber material? I've used Star-Brite Liquid Electrical Tape for many years which is a liquid rubber material and love the stuff! But I typically used a shrink wrap on top of it for durability where possible.

 

Never used Scotchkote. Is it a liquid rubber material? I've used Star-Brite Liquid Electrical Tape for many years which is a liquid rubber material and love the stuff! But I typically used a shrink wrap on top of it for durability where possible.

It's a hell of a lot better waterproof coating than a typical liquid rubber. I've had direct sea-spray exposed electrical connectors on antennas sealed with Scotchkote over a proper electrical tape layer look brand-new inside after years of service. Don't use it wearing good clothes as the stuff will never washout.

https://www.alliedelec.com/product/3m/scotchkote-fd/70266599/
It's not cheap.

 

I need to join a two conductor cable - 12V, 1A. The join will be submersed in 1m of rainwater.
I need a reliable way of doing this, please.

Hello there,

I would not trust any fix really without some sensors to test if it became faulty because you wont know it if it fails and still delivers current. DC in mineral water causes fast etching of most metals.

What i would do is find the ends that dip into the water and go back some ways from that, then cut the wire at both ends (decently far from the water) and replace the entire under water run with wire that has the proper coating for that. That will mean two splices but they will both be dry.
We did an underground run one time and that has to resist rainwater. The run was done entirely with one single wire no splices, and that was for 120vac 60Hz power. That kind of cable is super tough. This is of course if you can replace the entire run.

If i couldnt do that, i would look into conduit. You can get plastic or metal but not sure about what metals you can get these days. If you have to splice then it will be inside the conduit. That's means you can be sure it wont leak into the copper at some point unless something catastrophic goes wrong and that would take a lot. That is if you have access to the entire run.