Much effort is being put into large scale desalination to produce potable water but this idea is in a form that could be easily tried out on a small scale with readily available materials. The idea has much in common with the Solar Desalination Aquaduct proposed by [FlyingToaster], <ref> but this version
has more modest aspirations.
In simple terms: A length of black plastic pipe has its open start end positioned below the surface of a reservoir of non potable source water. From here, the pipe is laid out up a gentle slope for a length to be determined and then looped back down to the bottom level. The pipe will be heated by the sunlight. Source water is pumped into the pipe at a point near the top of the rising section of the pipe and trickles back towards the source water reservoir while heated air is blown in the opposite direction evaporating water as it progresses. The water vapour laden air is routed on through the pipe and down to a point where water can be condensed and collected.
In more detail: Ribbed black Plastic pipe of around 4 inches in diameter is widely available for drainage and ducting purposes and in significant lengths. For this application lengths of such pipe could be joined if necessary. The open end of a length of pipe is immersed under the surface of the source water which could be sea water or whatever is available. The pipe is then laid out up a slight slope for a length to be determined and then routed back downwards. From this point downwards the pipe could be shielded or buried to prevent further heating. The pipe is then immersed back in the source water for a length to be determined and then routed back to surface so as to vent to the atmosphere.
A second length of pipe has a small fan inserted into the open start end blowing into the pipe. This pipe is also laid so as to be heated by the sun and the far end is joined to the first pipe near the base. The fan is used to blow air through the pipe warming up as it flows into the first pipe. A small pump then feeds the source water into the first pipe at a point just below the high point from whence it trickles down towards the bottom against the flow of hot air being pumped through by the fan. Water will vaporise and be borne up the pipe and over the high point and then down to the point where the pipe is immersed in the source water which will act as a heat sink and condense some of the water vapour. The condensed water, hopefully of a useable quality, is then drawn out from this point by suitable means. The whole assembly is powered by solar panels. The throughput of feed water must be sufficient to preclude the build up of salts and deposits in the pipe. Solar powered Peltier cooling might make the condensation stage more efficient although adding complexity.
The concentrated 'brine' could simply drain back into the source water or be separated to allow further evaporation to produce bulk salt or even enter a separation sequence to harvest the various constituents.
One Solar panel would provide the power for the fan and small pump.
Such simple piping is likely to yield to UV attack after a while but, if the idea is proven, then more suitable material might be found and ways of enhancing the heat impinging on it deployed.
There are cases where simple evaporation is required such as where it is desired to concentrate low level waste water to a level where it is more economical to tanker away or be subjected to conventional treatment methods. In this case the pipe would be opened to the atmosphere at the top of the slope and the water vapour vented to the atmosphere.