[RE-wrenches] Off-Grid Whole House RO

Fri May 9 10:03:43 PDT 2025

Jason

  We have worked with customers that have gone the rainwater route. They take it off a roof and run it into a 1000 to 3000 gallon tank. Then they use a 1/2 hp pump through a simple but extremely effective 3 stage filter with an incredible UV filter. A lot less power used with very clean water.

Peter Giroux

ASAE

From: RE-wrenches <re-wrenches-bounces at lists.re-wrenches.org> On Behalf Of Drake Chamberlin via RE-wrenches
Sent: Friday, May 9, 2025 11:09 AM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Cc: drake.chamberlin at redwoodalliance.org
Subject: Re: [RE-wrenches] Off-Grid Whole House RO

Is using roof water and a cistern out of the question? 

Drake Chamberlin

Athens Electric LLC

Ohio Electrical Contractor’s License 44810

NABCEP Certified PV Installation Professional

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On 2025-05-08 15:36, Jason Szumlanski via RE-wrenches wrote:

Water pump is not my strong suit. I usually leave that up to the experts around here. Unfortunately, the experts are clueless when it comes to off-grid living. I have a client with a setup that is pretty unworkable. I'm trying to give him some general guidance. 

The setup uses a brackish water (might as well be salt water) very shallow well. It is about 3 ft underground for the water table. The RO system installer has a 1 HP 1.25 SF Century centrifugal surface pump drawing water from the well and pressurizing the inlet of a StaRite 1.25 HP booster pump designed for about 10 GPM at 150 PSI to run water through the RO system. 

Both of the pumps run simultaneously and continuously when producing water, and the water production is ridiculously low. I understand that RO production is going to be slow, but the amount of power these pumps are using is pure insanity. I have advised the client that, at a minimum, this system needs to be on a smart load circuit to run only when there is adequate battery capacity. The startup surgery is not a concern, but it does flicker the lights and it makes quite the racket. 

My thoughts are that the well pump is drastically oversized. The booster pump only needs 10 gallons per minute, and it has a suction head of 15 ft. I don't even know if the well pump pressurizing the booster pump inlet is required. I'm thinking we should be slow pumping water into an interim holding tank at least at the height of the booster pump. At a minimum, the well pump should be on a pressure switch with pressure tank so it can cycle. 

Can anyone give me some general guidance, and perhaps a VFD pump that does not have the startup surge and is maybe more efficient? During times of heavy use, the RO system can easily eat up half of the PV produced during a day at this site.

Jason Szumlanski 

Florida Solar Design Group 

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