The output is a closed relay so you need something to signal HS... you could use any of the usual suspects for that.

As far as the actual water detection, I just used figure of 8 speaker cable (cheapo stuff) and laid it under the tanks and also above the normal water level in the tanks so that the bare ends see the moisture or water if it reaches that level. All runs of wire are in parallel to the module.

So - nice and easy... and a very handy device for peace of mind... I set it up to email me if it sees water..... not sure what I will do if I get that email when on holiday!