From the air or from your bore­hole, here’s how to get self-suf­fi­cient

Popular Mechanics (South Africa) - - CONTENTS -

Get your wa­ter an­a­lysed

A de­tailed wa­ter anal­y­sis will be re­quired to as­sess the cur­rent wa­ter source. This will en­sure that you have ad­e­quate pre-treat­ment and also as­sist in choos­ing the cor­rect process for the in­tended use of the wa­ter. Our re­search put sam­ple test­ing into two cat­e­gories. If you just want to pipe bore­hole wa­ter for ablu­tion and wash­ing clothes, you’re look­ing at spend­ing around R3 000 at your lo­cal wa­ter test­ing fa­cil­ity like Aquatico in Gaut­eng or through the city coun­cil in Cape Town. This kind of test­ing also has a seven work­ing day turn­around.

To test wa­ter for the in­ten­tion of con­sump­tion you need to get what is known as a ‘full SANS’ done. This will cost you around R10 000 and there’s a 15 work­ing day pro­cess­ing time. Through this anal­y­sis you’ll get the full pro­file of your wa­ter to see how you need to treat it.

De­cide what you will be us­ing it for

If you are just us­ing the wa­ter for general house­hold ir­ri­ga­tion, de­sali­na­tion is nor­mally not re­quired. An in­ex­pen­sive fine fil­ter will be suf­fi­cient to pre­vent noz­zles from block­ing.

For house­hold tasks like wash­ing and ablu­tion, de­sali­na­tion is not nor­mally re­quired. The fo­cus here is to re­move heavy met­als and hard­ness that could dam­age plumb­ing and san­i­tary­ware. This can eas­ily be re­moved by ox­i­da­tion (adding chlo­rine) and me­dia fil­tra­tion (sand fil­ter).

For drink­ing wa­ter, it ad­vis­able that de­sali­na­tion is used; not just for re­mov­ing salt, but also as an ad­di­tional bar­rier against pathogens and other types of pol­lu­tants.

Know your en­ergy costs

The higher the salt con­tent, the higher the pres­sure re­quired to pro­duce potable wa­ter. Es­sen­tially more en­ergy is re­quired to pro­duce higher pres­sure and thus en­ergy cost will be higher.

At higher salin­i­ties, mem­brane foul­ing and scal­ing also be­comes an is­sue that needs to be con­sid­ered. Ad­di­tional chem­i­cals and dos­ing equip­ment would be re­quired to reach the de­sired min­eral con­cen­tra­tions.

Cor­ro­sion is a fac­tor at higher salin­i­ties. This in­flu­ences the ma­te­rial se­lec­tion of the pip­ing and equip­ment and ul­ti­mately the start-up cost.

Try har­vest­ing wa­ter from air

The In­cas built their set­tle­ments high above the clouds and har­vested dew to serve their wa­ter needs. While ef­fec­tive, these pas­sive meth­ods of wa­ter col­lec­tion have low yields com­pared to pow­ered so­lu­tions. On the pow­ered side, though, the story is a bit more grim. De­hu­mid­i­fiers use a cool­ing coil to cause con­den­sa­tion, so the process hinges on the cold­ness of the cool­ing coil and is ac­tu­ally more en­ergy hun­gry than pro­por­tion­ate de­sali­na­tion.

By far the most pop­u­lar so­lu­tion cur­rently is the wet des­ic­ca­tion method which uses a brine so­lu­tion to ef­fec­tively pull mois­ture out of the sur­round­ing air. Again, the brine must be pro­cessed – usu­ally heated to boil­ing point – and wa­ter har­vested from that process.

You could also try col­lect­ing the waste wa­ter from air-con­di­tion­ers. Har­vested wa­ter from this process still needs to be pu­ri­fied but at least the pro­duc­tion method is a by-prod­uct of a dif­fer­ent process.

Re­new­able en­ergy has im­proved the en­ergy cost of these al­ter­na­tive wa­ter-har­vest­ing meth­ods but it’s still rel­a­tively more ex­pen­sive than col­lect­ing and retic­u­lat­ing rain, or pump­ing from a bore­hole. Un­less you live in con­stant fresh­wa­ter fog, you should catch and treat as much as you can. PM





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