Tur­bocharg­ing your wa­ter har­vest­ing

The Shed - - Rainwater -

Har­vest­ing wa­ter at home can be a has­sle un­less you have a smart sys­tem.

In ar­eas with retic­u­lated wa­ter sup­plies, most rain­wa­ter-cap­ture sys­tems are sim­ple tanks at­tached to gut­ter­ing down­pipes. Sadly, there is not enough wa­ter pres­sure to make it re­ally use­ful. You can fill a wa­ter­ing can from it but it won’t drive a sprin­kler sys­tem, and un­less you have a de­cent fall on your gar­den that wa­ter is likely to be un­der-uti­lized.

If you are keen enough to in­stall a large tank and pump you can get de­cent pres­sure in your hose and you can di­vert tank wa­ter to the laun­dry and toi­lets as well as gar­den taps. But now it gets se­ri­ous, as you have to plumb in sup­plies to those parts of the house, and you have to be able to switch be­tween tank and retic­u­lated sup­ply when the tank runs low. Just think­ing about switch­ing back and forth man­u­ally — let alone re­mem­ber­ing to think about do­ing it man­u­ally — is ex­haust­ing.

That’s why Garth Co­hen at

White In­ter­na­tional, which sup­plies all man­ner of wa­ter sup­ply sys­tems, is such a fan of au­to­matic changeover de­vices. Th­ese de­vices, which con­trol the tank’s wa­ter pump, en­sure that tank wa­ter is used first to get max­i­mum ben­e­fit from it, then when the tank runs low, they seam­lessly switch in the mains sup­ply. Twenty-four hours later the ded­i­cated pump con­troller will check the tank level again, and if it has cap­tured enough rain­wa­ter it will start draw­ing from the tank again and the changeover de­vice then will switch back to us­ing tank wa­ter. Your tank wa­ter doesn’t get the chance to sit around do­ing noth­ing.

Garth says that th­ese sys­tems are top sellers in Aus­tralia where coun­cils have brought in rules that in­sist on har­vest­ing. They still make per­fect sense in new builds here, but in rainy New Zealand, most coun­cil and health au­thor­i­ties are more fo­cused on mak­ing sure un­treated wa­ter doesn’t get into the pipes sup­ply­ing potable (drink­ing) wa­ter. They re­quire back­flow pre­ven­tion de­vices (RPZs) in­stalled in sys­tems where changeover de­vices switch be­tween tank and mains sup­ply. And the non-potable sup­ply lines have to have dif­fer­ent-coloured pip­ing and sig­nage.

This may ap­pear baf­fling to peo­ple in ru­ral ar­eas who lit­er­ally live off tank wa­ter but they are more likely to have UV or other treat­ment sys­tems. Some may have con­di­tioned their immune sys­tems to lo­cal con­di­tions but health au­thor­i­ties also sus­pect peo­ple on un­treated sup­plies sim­ply have more un­ex­plained ill­nesses. And as for us­ing grey wa­ter from sinks and show­ers for gar­den wa­ter­ing or flush­ing toi­lets — both com­mon over­seas — coun­cils and pub­lic-health of­fi­cials won’t even set stan­dards, which, by govern­ment logic, makes it il­le­gal.

Sub­mersible pump for in-tank in­stal­la­tion

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