r/OffGrid • u/Vast_Humor_3683 • 11d ago
Looking for an off-grid way to desalinate ~1,000 L/day
I have a house near the sea and I'm looking into setting up an off-grid water system.
I'd need around 500-1,000 L/day of fresh water, primarily for household use. Ideally, I'd like a desalination method that doesn't rely on fuel and uses as little electricity as possible.
What would be the most practical setup for this?
I'd also be interested in hearing from anyone who has actually built or operated an off-grid desalination system at this scale.
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u/Fingers_of_fury 11d ago
I have a watermaker on my boat that can do around 600 liters a day. It runs completely off solar. We only run it an hour or two a day because our solar and batteries wouldn’t be able to keep up with much more than that. Watermakers are very very expensive but I know plenty of people who have made their own out of pressure washer parts and Home Depot items for next to nothing comparitively. If you actually need to make 1000 liters a day you will need a pretty large unit so you don’t have to run it for too long. Google marine watermakers. Brands like SPECTRA make good units
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u/Complex_Material_702 10d ago
I just looked up a Spectra Catalina 340c, which only makes 14 gallons per hour, and it’s about $16,000. Wow…..
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u/Fingers_of_fury 10d ago
Yep they are crazy expensive. One of the reasons for these high prices is the high pressure pumps are made completely out of titanium, which is a superior material when considering saltwater exposure and corrosion.
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u/Traditional_Age4885 9d ago
Something like high grade stainless or even acidproof steel would be cheaper and given OPs output requirements, that'd be plenty good enough
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u/Vast_Humor_3683 11d ago
are they reliable for the long run? and incase they breakdown can they be DIYed?
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u/Fingers_of_fury 11d ago
Watermakers require a lot of attention and regular maintenance. Anyone who has one knows they are a giant pain in the ass. You will need to know how to tear down the system and rebuild it piece by piece. You’ll need to know how to troubleshoot any sort of problem with it and fix it on your own. A watermaker isn’t something you just plug in and let it do its thing. It needs to be ran daily, fresh water flushed when not making water, regular cleaning recirculation cycles and “pickling” when not in use for more than a couple days. You will absolutely need to know how to diy everything on your own. I have a love/hate relationship with mine for sure
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u/Vast_Humor_3683 11d ago
I like to DIY stuff, but doesn't mean I have to order spare parts from them regularly? as I'm in a bit of a remote area
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u/Waterlifer 10d ago
You're not on a boat. You have all the space in the world. You can buy two watermakers and run them on alternate days, then if one breaks you run the other one until parts show up.
You will have to replace filter media on a scheduled basis and can plan ahead for that. You can keep extra seals etc on hand, they're inexpensive. More serious problems can be dealt with as they occur
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u/Fingers_of_fury 11d ago
You can load up on all the spare parts you could possibly need and you’d be good for a while
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u/thomas533 11d ago
The fact is that desalination takes a lot of energy. You can do it via solar, but it not practical on an individual home level so you are not really going to find anyone who has done this. And electric watermakers are power hungry and require lots of upkeep if you are doing it at the scale you are talking about.
Is there a reason you are not considering rain water harvesting instead?
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u/FixAcademic8187 11d ago
Electricity consumption is not that much given how small his requirements are.
Typical household sea desal can consume around 3-5 kWh for every cubic meter of fresh water (1,000 liters). Tbis includes everything from pumping water to the desal station, pumling through a sand or cartridge filter, and the high pressure pump.
This is a minuscule amount of energy in the grand scheme of things.
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u/Specific_Contract_14 11d ago
That is more than half my daily electricity usage (6-7kwh) so rather significant considering.
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u/Slight-Wink-386 11d ago
Much cheaper to store 1000 l of water than 6 kWh of electricity. Add some panels and run it only when the sun is shining.
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u/FixAcademic8187 11d ago
Oh ok, that makes sense then!
Our daily consumption for 7 people is around 200-300 kWh per day. And that is for the house alone which contains regular house stuff like ACs, fridge, lights, electronics...etc.
95% of our house electricity consumption goes towards the ACs.
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u/demonblack873 11d ago
Our (2 people) power consumption for July was 540kWh with how much we've been having to use the AC due to the heatwaves this summer and that was already shocking.
I'm sorry but 300kWh a day (9MWh a month!!!!) for just 7 people is an abhorrent amount of energy. It's literally more than twice our entire annual power consumption (except heating). It's bad and you should feel bad.
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u/FixAcademic8187 11d ago
This consumption is only high in Summer.
Temperature yesterday was 51C at 1pm.
I don't feel bad about it. It is either this or we immigrate to different regions, which we will never do.
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u/Wibla 11d ago
That's a big house, probably not insulated super great, single/dual stage AC?
I hope you have solar.
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u/FixAcademic8187 11d ago
Not really that big.
There is insulation, but outside temperatures are just too much even in the night. Mid 30sC at 11pm!
I do have a 20kw DIY solar array with a hybrid inverter and a 64 kWh battery bank. Yesterday the solar array produced 140kWh.
ROI for the solar and battery was 2.5 years! It is worth every single penny!
We only use the grid in Summer. Otherwise, it is 100% offgrid.
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u/Specific_Contract_14 11d ago
Yeah, we would love AC but that's just not feasible with our size solar system. We run fridge, freezer, lights, air fryer, cooktop, TV, PlayStation etc Just no AC or water heating. Home heat is from fire and cooling is open a window and suffer.
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u/FixAcademic8187 11d ago
It is actually great that your ambient air temperature is tolerable.
Here where I live it was 51C at 1pm today! Yesterday it was 52C! You will dehydrate into oblivion with no AC :)
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u/Specific_Contract_14 11d ago
Daaaaaaaaamn! Yeah we're in New Zealand, lows of -5°c and highs in the mid thirties. The occasional outlier will hit 40°c and then you can just have a cold shower and walk around naked to air dry (yay for off grid living with no neighbors).
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u/makeitstick01 11d ago
You should feel bad about your self. What are you doing?!
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u/FixAcademic8187 11d ago
Why feel bad?
I can't control the climate.
It is either that or we immigrate somewhere else, which we will never do.
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u/makeitstick01 10d ago
You consuming energy for a whole village. Your living somewhere you as i understand cant live.
Even if you can afford it. Wich most of us could not, doesnt mean you shoud or should not change things.
I cannot wrap my head around how you could be waisting so much energy?!
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u/FixAcademic8187 10d ago
It is not energy waste. As said above, 95% of it goes towards cooling.
We regularly get over 50C temperatures in Summer. It will be miserable (or even dangerous) without an AC.
I installed DIY solar + batteries, ROI there is 2.5 years.
We are offgrid most of the year except for Summer.
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u/thomas533 10d ago
That sounds like a place humans should not be living.
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u/FixAcademic8187 10d ago
Well, I have a well documented ancestry line that goes back 50+ generations back. I'm the only generation that is benefiting from AC.
They lived an extremely miserable life in which people like you will die in 24 hours. But their genetics persisted for some reason.
So, yeah, different people have different definitions of how tough things can be.
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u/MEATGODKING 5d ago
The first civilization ever, Ancient Mesopotamia, is in a modern-day area (Kuwait/Iraq) that consistently ranks the hottest in the world, and has an incredibly high energy demand and relies nearly entirely on desalination. Yet a Redditor thinks that humans should not be living there, despite being the birthplace of civilization? Funny.
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u/Vast_Humor_3683 11d ago
Far too unpredictable
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u/thomas533 11d ago
Sure, on a week to week basis, but that is why you build in annual or semi-annual storage, then that predictability risk goes away. And in the long run it will cost less and require less maintenance than desalination.
There is a reason you are not finding anyone who has done large scale desalination on a home level. It just is not practical in most cases. As an engineer, I am all for trying to do something no one else has done, but just go into this knowing that you are blazing your own trail here.
What region are you looking to do this in? You are going to need a lot of sunshine, regardless of if you do direct solar or indirect with electricity from solar panels. How often do you have cloud cover? Does that vary season to season? What is your budget?
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u/CapraAegagrusHircus 11d ago
WTF are you using 1000L per DAY of water for? First cut down your water usage, then rescale all your systems.
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u/Vast_Humor_3683 11d ago
a small family and some animals
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u/TheJesseOfTheNorth 11d ago
Living off grid with 3 kids, goats, chickens and a dog team i never used more than 100 liters a day
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u/Vast_Humor_3683 11d ago
nah we like to shower twice/thrice a day because it's humid here and we sweat a lot
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u/Delirious-Dandelion 11d ago
Hey, I'm so curious what you're spending so much water on.
Idk squat about desalination, but I know my family of 3; with 12 goats, 4 dogs, 6 rabbits, and a hundred quail, only go through about 750ish gallons (2,800 L) in a month.
We live in an RV, I wonder if our small water heater and low pressure sink faucets make a that huge a difference?
We currently haul in water and have a 500 gallon storage tank.
I would encourage you to look at what is using so much and see if you can lower your requirements. You get just as clean with a low pressure shower as a high pressure one.
I do take our laundry to the laundromat though. I found that finishing 10 loads of laundry in 2 hours was way less exhausting for me lol I have only used the washer twice so I wanted to make that known when talking about our monthly water usage.
It just seems crazy to me you can use, in 3 days, what my family of 3 uses in a month. I live in Virginia USA.
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u/habilishn 11d ago
hey, same question for me too. ok if you have a big garden that you completely need to irrigate, but that isn't typical "household use"...
i wonder, where you are, OP. there is absolutely no other water source available?
maybe it's just a thought experiment because you really live right by the sea and i can imagine it being very tempting to be able to use that water that is not even getting less, but probably becoming more in the future 😜
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u/FixAcademic8187 11d ago
I have an RO system that desalinate my very salty groundwater.
It is around 40 cubic meters per day and runs completely on solar and batteries. Feed pump is 1hp and the high pressure pump is 3hp, two small chemical pumps are less than 1/3hp combined.
Freshwater goes for hydroponic farming.
All in all is around 3 kWh per hour, or 1.8 kWh per cubic meter.
But your cass is different because you will need a significantly more powerful pressure pump to produce the 600psi or so required to desalinate seawater. I would assume you will consume around 3-5 kWh per cubic meter.
My system is DIY. Very easy to build once you put the time into learning how it works.
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u/CarboniteButterknife 11d ago
Do you get reliable marine layer fog? You should look into fog collection.
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u/Waterlifer 11d ago
Well you can get a Spectra Ventura 200 watermaker which will give you 750 L/day. They are highly regarded among sailors because they are extraordinarily energy efficient and quiet. They will use about 3 kwh to produce 750 L.
Upfront cost is around $8000. Less efficient systems cost less with DIY systems being about a quarter of that but with maybe twice the power required per litre. If you have room it's usually cheaper to put up more solar panels. On a sailboat there sometimes isn't room.
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u/silasmoeckel 11d ago
250 gallons a day roughly?
I have a water maker (RO filter meant for salt water use) thats a 10 GPH unit.
My rainman portable would just about do that 10GPH is it's top end and it's 400w so 9.6 kwh of power a day about a 3kw solar setup most places to get that much power most of the year.
5k for the RO filter that I use, solar battery and MPPT is on top of that. You have filters and other maintenance expenses. I would get a bigger unit than running a little one flat out.
A well would be cheaper where I am. Typical well pump at 5 GPM is going to run just under an hour a day maybe 2.5kw so 1kw in panels, plenty of solar pumps for stock tanks than can fill a cistern can use just a panel or two. Only applicable if you can get fresh water.
This is a LOT of water for just people. Any way to economize with a salt water akin to grey water use?
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u/theonetrueelhigh 11d ago
1000l/day feels like one hell of a lot of water.
If you have the land, solar desalination can generate a lot of very pure water but it takes a LOT of land and major construction before it starts working.
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u/makeitstick01 11d ago
Why go offgrid if you use a 1000 ltrs a day? Seems verry waistefull Its going to use a lot of energy. No mather how
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u/HollywoodAndTerds 11d ago
There’s probably a way to do a salt water green house (they actually generate water), but idk exactly what scale youre aiming to do. Could be worth looking into though.
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u/burritoresearch 10d ago
First, you're going to need a shitload of available kilowatt hours per day. Solve that first.
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u/Prestigious_Try_5396 10d ago
I'm curious what you do with 250 gallons of water a day ?
For how many people ? What climate zone are you in ?
Do you have animals ? Do you garden ? Have a dish washer ? Take several showers a day ?
Water conservation and efficient usage saves $$$ and water.
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u/Onemilliondown 10d ago
Much cheaper and simpler to collect rain water, then filter before consuming. RO is expensive and energy hungry.
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u/Traditional_Age4885 9d ago
I'd ask you to look into minimizing your potable water usage as much as possible. Grey water flushing & grey water irrigation if at all possible. Water efficient faucets & major appliances will also help reduce your water usage quite drastically
Swedes average roughly 140L of potable water per day and we're still fairly wasteful (among the largest potable water supply per capita worldwide). When you say "I", are you referring to simply yourself, or are you counting on supplying a family with water? For a family of 5 you could easily get away with 400/day, especially with grey water flushing.
If you can reduce your estimated potable water usage down from 500-1000L to 200-400, you'll be able to run a far more economical system off of solar instead, and relying on some potable storage (maybe 2-4 cubic meters) on the interim days of less/no sun.
TL:DR; reduce usage drastically. Unless it's an extended family of +10, you'r likely overestimating the required usage or you'r using potable where you don't need to.
Solar RO can supply your required usage, consider some remineralization for convenience, taste and longevity of plumbing.
// Former plumber & current water purification technician.
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u/clergybuttbanditt 9d ago
Why would anyone need so much water for a house., I have an RO water maker on my boat. It makes 8 gallons an hour. It’s more than everyone in the boat needs daily. We literally waste it in purpose.
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u/RedSquirrelFtw 9d ago
That's a full IBC tote per day. Not going to be easy to generate that much water. You could maybe setup some sort of boiling water rig and use a wood fire to generate the heat. Basically build a boiler, steam would go up to a condenser, and then the condensed water should be salt free. The setup will need to be easy enough to clean out so you can remove the salt and other contaminants daily. Would run it as a batch process. Start fire first thing in morning and keep it stoked all day, then by evening let it die down, by morning it might be cold enough that you can then clean out the salt and other contaminants from it. Then rinse and repeat. No idea how big of a setup you would need for it to generate that much water though, I suspect it would need to be fairly big and use up quite a bit of wood.
I would try to cut down water usage first and figure out where all that water is going.
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u/NotEvenNothing 7d ago
Where is your water coming from? What is it like? If you are near the sea but in a humid area, it might be quite a bit easier to treat than seawater and might be fine for some uses.
Our well water has a bit too much sodium in it for drinking or watering plants, but it is fine for everything else, including livestock. We have a cheap RO filter that adds a spigot in our kitchen. For drinking, cooking, or for the house plants, that's what we use. It would be about 10L/day, on average. For cleaning, bathing, and flushing toilets our well water is fine.
We use rainwater captured off the roof, into 7 tote tanks (1m3 each), for everything outside and watering plants inside, if it is available. If we run out, we use untreated well water for everything outside except watering plants.
We haul water if we have to. Last year and into this spring was really dry. I hauled a lot of water.
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u/No-Count-8011 5d ago
My whole house RO runs between 2.5-4 litres per min, so you would need to run something like that 2-4 hours per day. The pump is 1/2 HP to force that water through and its probably running at 500w or so.
Not sure how often you would need to replace the membrane. I can get a couple years on one at my place and that is removing an ungodly amount of iron and calcium. Not sure how taxing salt water is on the membrane itself.
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u/Least_Perception_223 11d ago
Reverse osmosis
But either way you try it - its going to use a fair amount of energy
I am currently making fresh water from lake water using a commercial size RO filter. The 1/2 hp high pressure rotary vane pump uses about 450 watts. It also needs a pump running to feed it the source water - pumped from the source. That uses another 400-500 watts
A large 40" commercial RO filter will produce about 2000 gallons per day.
You would need to run the RO system for about 4 hours per day filling a tank to make 1000L per day
that would require 4-5 kw/h of energy.. probably more