1. Skip to navigation
  2. Skip to content
  3. Skip to sidebar

DRP #1: Watermakers

Home Forums Archive Distributed Research Projects DRP #1: Watermakers

This topic contains 20 replies, has 10 voices, and was last updated by Profile photo of Thorizan Thorizan 6 years, 11 months ago.

Viewing 15 posts - 1 through 15 (of 21 total)
  • Author
  • #750
    Profile photo of

    Given that the goal of a seastead is to live long term out in the ocean, it is desirable to minimize the amount of stuff that needs to be imported. Given how bulky fresh water is and how available salt water is, it makes a great deal of sense to contemplate converting salt water to fresh water on site. Apparently, the commonly used term for these devices is “watermaker”.

    What we need to figure out is 1) what watermakers are on the market, 2) their approximate cost, 3) their energy requirements, 4) how often they break, and 5) what does it take to get them fixed. If people have first or second hand experience to share, please do so.

    To the best of my knowledge, the two primary methods of desalination are 1) reverse osmosis and 2) thermal desalination. If there others, please let us know. We are focusing on smaller seasteads here — 1000 to 6000 square feet of enclosed area. Furthermore, we need to understand how much water people need for drinking, washing, toilet flushing, laundary, showers, etc.

    Anyhow, that should kick of the topic.

    Profile photo of

    Weren’t you the one who said in essence that everything we need can be bought at West Marine? :) West Marine sells yacht-sized watermakers from $3000 to $11,000 for 40 gallons per day to 700 gallons per day. The Katadyn ones appear to be about twice as energy efficient than the other ones due to some kind of pressure-preserving arrangement, but are on the small end of the output ranges. All are based on permeable (fiberglass?) membranes (reverse osmosis) and electrical high pressure pumps. Apparently it’s possible to damage the membrane if used incorrectly. All feature extensive filtering of the intake seawater to prevent failures from happening.

    Large ships presumably use steam or vacuum vapor distallation since they can operate on a larger scale.

    In both cases the key factor is energy. It takes energy to desalinate water using these mechanical means, either to heat steam or generate high (or low) pressures. The machines also require some maintenance.

    A low tech approach is to trap water vapor rising from the ocean and collect it. The water vapor by definition lacks most of the salt.

    Figure at least 10 gallons of water per person per day. Landlubbers probably use several times that amount.

    Profile photo of vincecate

    We have a wiki page on fresh water:

    But for a Single-Family-Seastead I am very happy to just buy something at West Marine:


    As for reliability issues, I would buy 2 watermakers and also have a tank of fresh water large enough that in an emergency it could last my family a month. Maybe 2 of these 55 gallon plastic barrels that I can get for $20 each.

    A 40 gallon/day watermaker draws 4 amps at 12 volts. So 48 watts. This is not much even for solar.


    It really seems like fresh water is a solved problem. When it comes time to outfit our seastead we can look at what is for sale and then buy something. There are many real problems that have to be worked out before seasteading will be real, but this is not one of them.

    Profile photo of

    48 watts is a measure of power, not energy. It’s energy that’s the main budgeting factor. 48 watts for 24 hours is 1152 watt-hours of energy. A single 150 watt solar panel could produce that from 8 hours of a sunny day. In principle the 40 gallons of water produced from that could be enough for 4 people.

    I agree that watermaking is solvable by using commercial off the shelf components and therefore is mostly a non-issue.

    Profile photo of

    Some data for my previous post, the USGS found that Americans use 80 gallons of water per day: United States Geological Survey, U.S. Department of the Interior, Estimated Use of Water in the United States in 1995, U. S. Geological Survey Circular 1200.

    The Katadyn rated for 6.7 GPH uses 216 watts while operating or 216 watt-hours to make 6.7 gallons, which is 32.4 watt-hours per gallon. At 10 gallons per person per day, that’s 324 watt-hours-per-person-per-day. So a water budget really turns into an energy budget. 80 gallons per day would be 8 times that, but Americans probably water lawns, have inefficient toilets, etc. In any case, water requires energy; the main question is how much.

    The biggest energy cost of distillation is probably going to be for heating the water, typically by fuelling a boiler with oil (at sea) or natural gas (on land). One could also use solar energy to heat water, and maybe the remainer of heat and pumping using electricity. Solar energy is ideally suited to heating (water). It’s very efficient at that application.

    Profile photo of Eelco

    80 gallons? How is that calculated? Does that include water used for growing their food, for instance?

    Profile photo of

    I should have provided a reference:


    Profile photo of

    Thank you for starting the fresh water wiki page. That is where I am going to summarize this discussion. Until I added the three lines on the Katadyn products, there were no entries on reverse osmosis. There are still no entries on thermal desalination. It would be nice to discuss rain water collection as well.

    If all products worked as advertised, the world would be a much better place. The only person I have talked with who has first hand experience with watermakers said that they had two of them and that they basically did not work in their situation. This was Ryan Lackey who was living on Sealand at the time. He said that there was too much silt in the water and it caused them to clog up. They ultimately just had people bring in water.

    I would like to see some comparison between the reverse osmosis and thermal desalination. Somehow, I do not think thermal desalination has as many problems with silt as reverse osmosis. For deep sea seasteads, silt is not much of an issue. For seasteads that travel around the Carribean islands, I am not as sure.

    I picked on watermakers for the first topic because I ultimately think that this technology will be purchased off the shelf. I do not know which technology will be purchase though.

    It is still important to figure out the energy trade-off issues associated with them. For example, the capacity of the Katadyn systems is not linear with cost — $2999=>1.5gal/hr, $3899=>3.0gal/hr, $4299=>7.0gal/hr. It might make sense to increase the solar collector some, buy a larger watermaker, and only run them during daylight hours. Would a solar still have a similar footprint and be more reliable?

    We also need to figure out water requirements. How much water storage do we need?

    If you have answers to all of these issues, please post them up and we can move onto the next topic.

    Profile photo of Joep

    For people that haven’t read the book beta yet, there is quite a lot of information here: http://seasteading.org/seastead.org/commented/paper/infra.html#Water

    Profile photo of vincecate

    The optimal decision for which WaterMaker to buy will have all different numbers when we are really ready to buy. The cost of solar will be different, the cost of batteries will be different, the selection of watermakers to choose from will be different. And we don’t really know the usage. Is it for a family spending several million on a seastead or a family spending $50,000 on a seastead? It seems silly to try to optimize this decision now.

    There are thousands of boat users who use watermakers all the time. The Island I am on, Anguilla, gets all the Government sold water from a reverse osmosis plant. They did shut it down for awhile after the hurricane because the ocean water was too dirty. But the rest of the time this has produced lots of water for the island. In general Caribbean water is among the clearest in the world. Also, the big hotels here have their own reverse osmosis plants and they seem to work for them. There is a golf course here and it is using lots of water, all of which comes from reverse osmosis. There is a water bottling company in Anguilla and they use reverse osmosis to make the pure water they put in the bottles. Just because the Sealand guys had trouble does not mean much. Reverse Osmosis is a well established and well understood technology.

    I have not heard of anyone using anything else other than reverse osmosis and rainwater collection to get fresh water. At least 99% of the homes here collect rainwater.

    Profile photo of

    I ran across a web page where somebody describes how he built a watermaker from parts . First, this article gives a level of insight into the construction of watermakers. I certainly do not propose that anybody follow in this persons footsteps, though. Second, he makes a pretty strong case that inexpensive filters are just as good as the expensive filters designed for a specific watermaker.

    What I have not been able to figure out is how often people feel they need to change the filters. I know it depends on location, but so far my searches have come up empty.

    Profile photo of

    The reason for the topic of the week is to identify each need for a complete seastead and identify solutions in an orderly manner, along with sourcing, cost info and engineering info. While you may consider the problem solved, or the current information not applicable for use sometime in the future, it is very useful to have as complete a design as possible and to always have at hand an estimate for the cost of the project. By presenting a topic to focus on, this encourages the information to be consolidated in one convenient place for harvesting into the wiki and a database, rather than having it scattered all over the forums.

    No problem is ever completely solved because there is always a better way of doing things.

    Profile photo of

    Regarding silt, check out the West Marine catalog pages on watermakers. Seemingly half of the items sold are pre-filters and booster pumps to filter out as much silt and solids as possible before the membrane. So it would seem that pre-filtering is pretty important. The stuff they sell is based on a lot of experience.

    Every commercial reverse osmosis or steam distillation machine I’ve seen has extensive cartridge pre-filters, and they’re changed pretty often.

    That said, Sealand may have had more silt than the open ocean, given that they were in the delta of the Thames river.

    Profile photo of

    The West Marine advisor document on watermakers includes some general maintenance instructions, including flushing the prefilters with freshwater periodically, replacing o-ring seals on a schedule, cleaning the membrane, etc.

    In addition, some of the watermakers include pressure gauges probably before the membrane and before the pre-filter. If the pressure drop goes up too much, presumably something is clogged and in need of flushing, cleaning or replacing. (Pressure drop can be seen by noting the usual versus current operating pressures on the gauges, i.e. how much pressure is lost going through the filter.) In other words, measurements can help show when maintenance is needed.

    Profile photo of Patri

    I agree this isn’t a crucial topic, but it seems like a good warmup. Feel free to add more topics to the topic list.

Viewing 15 posts - 1 through 15 (of 21 total)

The forum ‘Distributed Research Projects’ is closed to new topics and replies.

Posted on at


Written by