Water Systems For the Small Seastead/Homesteader Philosophy

(Larry G) #1

This thread is to organize some of the previous thoughts that have been expressed for water systems in small seasteads:

In keeping with the “Two is One, one is None” philosophy, the figure above demonstrates multiple input sources and redundant methods as well as redundant equipment.

Example: Primary desalination by Reverse Osmosis using electrical system, with Backup Desalinator using mechanical PTO (power take off) from a diesel engine that simultaneously provides electrical generation (loading the diesel genset actually makes it more efficient). While it is entirely possible to use one Desalinator system with both an electric motor and provide a pulley for PTO to run it if the batteries are dead or the electric motor burns up, having fully redundant systems provides a measure of safety over and above that some Seasteaders may find desirable.

Example: Dehumidification drainage is an important part of environmental systems in tropical and sub-tropical climates. This is freshwater (even tho not potable at the point of collection) and should not be wasted. Draining condensate from roof units into the same rainwater catchment system should be easy, cheap and effective (at several gallons per day minimum per HVAC unit in the tropics, a unit could potentially provide one person’s entire minimum ration daily).

Using potable water only for those applications which come in close contact with the body and potentially affect health is just common sense. So provision is made for a saltwater “rinse” process for things like washing down decks, pre-showering with a separate freshwater rinse (and drain), even washing vegetables prior to cooking can be done with seawater.

Multiple effluent streams also make sense. The risk posed by each stream is different and cost to treat everything to the highest standards isn’t really justified. One thing missing on my diagram is an arrow showing some graywater output laterally to the blackwater system for flushing purposes.


Pre-rinse with saltwater and rinse with fresh contaminates freshwater with salt…

Condensation to potable water is going to be necessary, as is reverse osmosis.

I’m in a moderate to light humidity environment, now. Each ac collects several gallons of water, daily. At sea, I fully expect that running ac could potentially provide most of the potable water for a small family.

(Larry G) #3

Different effluent streams. See (updated) flow diagram and last paragraph.

Deck rinse with seawater, take a quick wash of the body there. This effluent goes back into the ocean.

Then you go into the freshwater shower. You’re already mostly clean, this allows you to quickly finish washing and rinse in fresh. The minor amount of seawater dripping off your body into the freshwater graywater stream is less than salt spray is going to get into your system anyway.

I haven’t been contemplating graywater introduction back to the desalinator, but I suppose it could be done. I’ve been envisioning graywater discharge to aerobic irrigation or hydroponics using halophytic varietals selected for mild to moderate salt tolerance. If you live by/on the ocean, you should try to grow things that like tolerate being near the ocean rather than the most delicate of salt-hating land plants.

I’m also thinking the low temp evaporation (dewvaporator) solutions will have a place. “Sailing the Farm” has some really low tech, easy to implement ideas on catching condensate.

As I posted about the other day, I’ve also found mini-split heat pump HVAC solutions that are designed and optimized for off-grid DC and hybrid AC/DC operation on primarily Solar PV systems. these systems produce a lot of condensate as well.

(Bob LLewellyn) #4

Heat pumps use a lot of power and every time you convert from one energy to another you have power loss. In the Caribbean there is plenty of sun and a solar distiller will be a good back up if you run low but there will be enough rain water that you will probably never need to use the solar distiller.

There is an article on watermakers and different methods to accomplish cleaning the saltwater.


Everytime the subject of fresh water came up, people always talk about methods that require the use of energy. What’s wrong with just gathering and filtering rainwater? It simply means the building design needs to be optimized for collecting water and may look strange but it’s doable. Natural islands have been doing it for millions of years. Difference is, we have the technology to store a lot more fresh water than an island of equal size can without contamination from sea water.

(Larry G) #6

On the contrary, heat pumps are one of the most efficient means of controlling temperature. The benefit is you aren’t converting from one form to another, you’re simply moving it from one place to another. Yes, it uses (rather than loses, a matter of viewpoint) energy to do so.

I have lived in the tropics and subtropics. One of the reasons they are under-developed compared to the temperate zones is because you simply cannot be consistently productive in those temperatures. It is actually dangerous to do much more than lie around in the shade without temperature controlled environments.

Shiina’s point first: nothing is wrong with collecting it, but it is not sufficient to guarantee life of multiple people who are hours or days from help. Minimum to sustain life is about 1 gallon per day per person. Two days without it and you will be a raving maniac who would drink a stranger’s blood to live. You can only go about 3 days without water before you are not only ill, but you die. Water is one of the primary determinants of habitability on remote islands, and the vast majority of the Pacific and Caribbean Islands have official water concerns, despite the rain. Water deserves significant planning and redundancy.

Now Bob’s point and Shiina’s second point: It takes significant storage capacity because rain doesn’t happen in the same amounts spread perfectly every day. You have to catch as much as you can when it comes. Storage capacity means weight, and volume that has to come at the expense of buoyancy and volume that could be used for other things.

Passive systems are great for energy efficiency, but you need a reserve capacity and safety factor of 3 times minimum requirement for real long term security, which means active systems that can kick in to make up shortfalls. This includes a duration, not just an amount, i.e. minimum comfortable capacity for x persons for x weeks. If you’re not planning in these terms, you’re failing to plan.

Islands have different freshwater systems, not all the same. You can have volcanic lakes (filled w rainwater), you can have low-lying areas that impound rainwater, you can have a combination of these and enough cracks in the rock structure to make springs appear in different places.

Low-lying coral islands and atolls tend to have none of that. Partly because, with no igneous, solid, elevated ROCK they don’t pose enough of a barrier to passing water-laden wind to force precipitation due to altitude & temperature/pressure differences.

What they do often have is a “freshwater lens” In the case of Tuvalu, famous for suing the Czechs for global warming, their wells now have brackish water, which is often referred to as “seawater contamination”. However, the basic hydrology of the way a lens works shows that it is not saltwater “intrusion” “contaminating” the freshwater lens, it is simply that there isn’t enough freshwater left to displace the saltwater that otherwise naturally infuses the sandy coral soils.

A lens requires some kind of barrier to mixing, and will accumulate as long as withdrawals (human uses, evaporation etc.) don’t exceed the rate at which the freshwater is supplied rain, minus the edge mixing with seawater. It’s a slow-ish process. It took ~160 years to turn the ~11sq km of Clipperton Island’s saltwater lagoon into a freshwater lagoon (for the top 20 meters or so) through accumulation of a lens. Of course, there is more mixing when rain is landing on a trappe dbody of salwater than when it lands on seawater-soaked sand and soil.

I think it is feasible to create an artificial lens on a relatively small scale for fun and profit. If you had a thick-walled tank submersed in seawater, even of a relatively high porosity concrete, and you kept it filled with freshwater, likelihood of “seawater contamination” is very low as long as the basic integrity of the vessel is intact. Micro cracks = no big deal. Macro cracks or holes would be a problem.

The thing is osmosis works in one direction at normal pressures. Less dense freshwater “tries to” dilute denser seawater. Not the other way around. So migration is outward from the vessel to the salt, not from the outside into the fresh. You might “lose” a tiny percentage of your freshwater to osmotic diffusion through the semi-porous container to the sea.

(Bob LLewellyn) #7

Going with the ‘Water Systems For the Small Seastead/Homesteader Philosophy’, collection of rain water would be easier and more plentiful for a floating stand alone barge than for a boat that has the ability to move a lot. We can extend the collection area by utilizing the available areas adjacent to the barge.

Hell, we can make a barge for collection and storage with the deck doing double duty of solar collectors for energy that sits in an indent so when it rains the water is caught in those indented areas and drained into the holding tanks below. We can make as many of this self contained water collection mini barges as we like. Each barge would also have a DC sump pump to refill the homes storage tanks and sell the excess to boaters that don’t have a watermaker.

(Larry G) #8

Absolutely. Some systems don’t have to reside in the same monolithic “real estate” as the people. Even for the homestead size seastead. After all, stabling the livestock in the house hasn’t been common practice for hundreds of years, pump houses on farms are generally located some distance from the sleeping quarters, and lots of other functions are separated from each other for various reasons. Water doesn’t care about comfort ad neither do solar collectors.

Compensate for “free surface effect” with baffles and the barge can be in the wave zone even if you want your residents to experience less acceleration.

(.) #10

It seems to be that the California water shortage is a myth at this level.
Local municipal water districts are against seawater desalination.
(youtube recordings of Laguna Niguel water district public discussion)
As soon as a water desalination project kicks in the “officials” declare that
there is enough water. When the project goes belly up the "officials"
declare water emergency. It is just a game.

Lots of more people could move to California, but there is not enough water for that, I think. The largest amount of water used, in my opinion is,
for flushing the toilets. Seawater could be used for that.
I think, when/if that is worked out, California could experience a population
growth. The only problem is that; nobody is interested about population
growth. There are enough people in California.
I have no problem with population growth. I think it would strengthen the economy.
But my opinion does not really matter. I would like to orient toward off-shore
technologies and off-shore living.

(Larry G) #11

The problem with using seawater for flushing toilets is that it is really, really hard on the systems for treating black water and prevents using natural biological processes as effectively. It would require an immediate and complete, very very expensive retrofit of every waste treatment facility and ALL of the distribution systems to every household and business.

Not at all practical, and wouldn’t help for inland locations anyway. It would be more expensive to bring seawater there than what we’re doing now.

But we REALLY shouldn’t be treating every single drop of water intended to flush toilets, wash cars, water lawns etc. to potable water standards. We also shouldn’t be treating every drop of graywater as toxic waste. It’s extremely wasteful of resources.


One of the best strategies for saving water is to keep from making much blackwater in the first place. Gray water can generally be run through a gravel titration bed, aerobically treated, filtered and made clean far more easily than blackwater sanitation and recycling.

Currently, I am living in an RV with a “Nature’s Head” composting toilet. I have worked out a scheme for further composting, using aa available composted, so that compost is completely sanitary, before utilization for gardening.

In addition, the toilet separates urine for other means of disposal. Paper/plant-fiber can be broken down for use in a co-digestion system for biogas production.

Once I have the equipment, I will be making a biogas digester to use the urine and rye straw, and paper wastes, plus food wastes and pet wastes, to make both biogas and liquid fertilizer, as well.



You now know I’ve invested over $1600 into the effort, and am committed for the plastic welder and supplies for the digester. I AM putting money toward seasteading. Pick a system, make it work SAFELY, build on that.
Doesn’t matter if you have a different opinion… BTW, the Nature’s Head is also USCG, and internationally approved for vessels, because it does NOT dump raw sewage… My additional choices are also for sanitation purposes.

The supplies and equipment for the digester will rapidly approach $1k. Once proven, the digester becomes marketable, and having the tools to replicate it reduces cost of copying and selling them.

I dunno, but pick an essential biological process, design around it, and sell accordingly…? Sounds like a business plan, but what do I know? I’m just a multiple college and university dropout, that advises on projects around the world… Maybe I missed something…

(Larry G) #16



Life changes the timing on things… Took a while, but that plastic welder and supplies HAVE been ordered and shipped… :sunglasses:
Due in by Aug 8th. May have an initial waste water system built by the middle of September. :crazy_face:

(system) #18

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