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Community and Q&A

Low energy use high flow water filtration for off grid applications (UV or otherwise)

moe_wilensky | Posted in General Questions on

A bit off topic perhaps, but I’m hoping someone on here has some experience with water filtration that I could leverage.

We are building an off-grid campground and will be taking water from a creek so will need some sort of filtration system for our guests’ drinking water. The water is crystal clear and runs straight down from the snow pack and we drink it all the time to no ill effects (and we will be running it through a sand filter) but, out of abundance of caution, we are planning on installing a  filtration system serving the central toilet and kitchen facilities.

My initial thoughts (and still the way I’m leaning) is a UV filter but, based some preliminary research, it looks like most UV filters run the light 24/7 which (at the peak draws we need to meet) seems like a good way to waste limited solar resources.

I’ve found some smaller on demand LED based units but nothing with the roughly 15-20 gpm peak filtration rates we’re targeting. Does anyone have familiarity with larger systems that will run only when water is flowing?

An alternative is to buy a smaller unit and store the filtered water but this might end up with a pretty big tank and, if I’m going to go to the trouble of installing storage, I think I’d still like a larger intermittent system so I can I can charge the storage when the sun is shining and the batteries have a high state of charge.

Anyhow, any thoughts on low energy use filtration approaches (and or recommendations for high flow intermittent UV filters) would be appreciated.

Note: the system has plenty of water available (though water conservation and effluent disposal is a concern) at about 60 psi.

Thanks in advance.

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  1. Expert Member


    I was licensed to oversee small water systems for years. Sorry I don't have answer to your primary question but will offer this advice:

    - First find out what permits and approvals you need. Up here in BC you can't supply water to more that two houses without registering with your health department.

    - Water treatment isn't something you can design based on the water looking clear, or tasting good. Get the water tested. You can then tailor the treatment to whatever threats it may pose. It will tell you what level in microns you should be filtering to, whether there is a potential problem with Gardia which needs UV, what the coliform count is and if chlorination is necessary.

    1. moe_wilensky | | #2

      Thanks Malcolm,

      I am, unfortunatly, quite familiar with the water license application process in BC, submitted over 3 years ago and still waiting for a response (which is what I was told to expect at the time of submittal, who knows what the delay is now). I am hopeful though, as there are currently no other licences on the creek, nor does it pass though any private properties other than our own before joining a river. We definitely planned to get the water tested, but i see you point about that informing filter/treatment design so i may move that one up the list of priories. Thanks for the response.

      1. Expert Member
        MALCOLM TAYLOR | | #3


        Yeah, it's a bit of a mess most places. That's a big part of the reason I let my license lapse. Luckily we are close enough to Vitoria that the bureaucracy works quite well here. I'd keep a paper trail of your testing and treatment choices for when they finally get around to dealing with your system.

  2. Expert Member
    BILL WICHERS | | #4

    I like to say that gov't exists to make things take too long and cost to much. They are pretty good at keeping records though, which will help them to fine you lots of money later if you bypass the permit process...

    In my area, you generally can't use surface water for drinking. I'm not sure if that's a hard and fast rule, but it's certainly very much discouraged. They want you to use a well, which lets the Earth act as a massive sand and biological filter. If you don't want to drill a well, and you have a stream, you might see if your water table is high enough that you could use a driven well (i.e. pipe + sledgehammer + effort = water well), then use a jet pump to pump the water out. Driven wells are only useable down to around maybe 20-30 feet or so under normal conditions though. These are the wells that used to be used with pitcher pumps back in the day.

    For filtering, I agree with Malcolm: you don't know what you need to do if you don't know what you're starting with. You probably want at least a fine particulate filter, but that won't be enough if the water is contaminated.

    UV filters could be tied in with the water supply, so that they only run when water is flowing, which would usually mean you'd want them between the pump and pressure tank. The downside is that it's possible for stuff to "sneak past" the UV lamp when the lamp is off and water isn't flowing, since the water that hasn't passed through the lamp yet hasn't been treated. That's why you generally keep the UV system running continuously. That's a big energy drain for an off-grid system though. You could potentially use a low wattage low flow UV system and treat the water slowly while storing it in a tank, but otherwise you're stuck. You do NOT want to trade off safety for efficiency here. Usually if you need a UV system, there is a good reason for it due to some biological contaminant in the water.

    I think your life will be easier if you can drive in a well and avoid using surface water. Keep in mind that surface water might vary through the seasons too, so it might be more contaminated at some times of year than others. You can't use a taste test to gauge if the water is safe or not, and just because you drank it and were OK once, doesn't mean you can count on it being safe the next time.


    1. moe_wilensky | | #5

      Thanks Bill, that all makes sense. While loads of folks (possibly the majority of the population in our valley) just drink surface water around here in the West Kootenays of BC, I agree that in a commercial context this is not a good idea without treatment. A dedicated drinking water well is for sure an option but were only going to go that route if we can't deliver acceptable water quality from the creek (we still need the creek water for irrigation and fire suppression so were taking a phased approach to see what happens). Thanks for your input.

  3. walta100 | | #6

    From a liability point of view, you would be crazy to serve paying customer’s surface water.

    Just because you tested the water an hour ago how can you be certain that it is clean now?

    How can you be sure there are no beavers up stream?

    One sick child and you would likely be ruined and a dead child could land you in jail.

    Haul the water in or dig a well.


    1. moe_wilensky | | #7

      Thanks for your input Walta. I was never considering having untreated drinking water. Just had questions about an energy efficient way of treating it.

    2. Expert Member
      MALCOLM TAYLOR | | #12


      75% of the water consumed in North America - some (237,000 Million gal/day) is surface water. The methods of ensuring a clean supply are well known. This isn't something novel.

      1. Expert Member
        BILL WICHERS | | #16

        True, but the very large scale treatment plants used for most of that surface water are rather more complex than most people run on their home systems. With a well, you have less potential issues you need to worry about on the treatment side.

        For the other posters, Malcolm is spot on in post #15. Filtration, UV, and chlorination aren't all the same thing, and serve different purposes. There are all kinds of other things that can be done to treat water too, so I mean "treatment" as a generic catch-all term that includes everything. It takes more to safely treat surface water to make it safe to drink than it usually does to treat well water. Some wells need nothing, some just a sediment filter. Surface water pretty much always should have some type of biological treatment too -- which means some "kill step" that kills little beasties in the water that might make you sick. There are lots more potential beasties in surface water than there are in a typical well.

        For the OP: I can *guarantee* you that if you look at that surface water you've been drinking with a microscope and a well slide, there will be all kinds of little beasties swimming around in it. Some of those beasties won't hurt you, some will only hurt you under certain conditions, but some will nearly always make you sick. Always remember that nature doesn't play nice, you need to be careful.


        1. Expert Member
          MALCOLM TAYLOR | | #18


          My house is serviced by a fairly small surface-sourced community water system with filters, UV and chlorination. It's remarkably similar to the the single house package my friend up the road has to treat his water supply fed by a creek. The only real difference is scale - and the testing and reporting the multi-user system requires.

  4. gusfhb | | #8

    At some point is a well cheaper/easier?

    1. moe_wilensky | | #11

      Very possibly at some point yes, but we'll for sure use the gravity fed water, even if we need an alternative source for drinking water. We'll also use it to serve a future personal dwelling (i drink out of the creek every day and all seasons, so I'm not so concerned about it).

  5. rockies63 | | #9

    I would put in a smaller system and store some water in a tank. Just in case the electricity goes out and you can't pump anything you'd at least have some water above ground. One thing I've heard that preppers and homesteaders do is to put an on-demand UV light on the incoming pipe and then have a backup light in the holding tank that operates on a set interval just in case something slips past the first light (those lights can get covered with "gunk" sometimes or the water can be so cloudy that the UV rays don't kill everything).
    A few questions:
    1. How are you heating your water?
    2. What are you doing about water for fire fighting?
    3. You mentioned effluent disposal being a concern. What are you doing for black water, grey water, etc? A septic system or outhouses or both?

    If you are using a septic system you might consider an Ecoflo system which uses a secondary chamber to really eliminate a lot more contaminants from the effluent. It also allows you to install a much smaller septic system.

    1. moe_wilensky | | #10

      Rockies, i do like the idea of storage, we've got a decent solar system and I've always enjoyed the idea of "storage of services" aka "making hay while the sun shines" to avoid excessive reliance on battery storage. That is, in fact, what I hope to do for hot water, large tank and a tempering valve attached to a high temp capable air to water heat pump that is set to run when the batteries hit a certain SOC.

      The long term goal is no fossil fuels, which will probably mean a wood boiler for DHW and heating in the winter but we don't expect to operate in the winter for a few years yet.

      For fire suppression, were setting up a ring of sprinklers (served by the aforementioned gravity fed creek water) around the key infrastructure combined with fire breaks and fuel management, won't be perfect but might minimize damage. We're lucky enough to have multiple water sources on the property, so well also build some ponds that we can pump from as a back up, but given our remoteness, the likelihood that someone will be around to fire up the pumps is limited.

      We went for simple on the black water, just a type 1 gravity system, we've got the land and the soil is good for it, grey water is just going to be mulch basins, we'll also have some outhouses for the more far flung sites.

      it's quite the project, something new every day...

  6. rockies63 | | #13

    You're in the Kootenays, right? I contacted the building department in Nelson a few years ago asking about composting toilets and they wouldn't allow them (even though they are legal throughout BC). The building inspector said they couldn't trust that people would operate them properly so it had to be a septic system, no matter how far out in the wilderness you are located.

    I hope you're running everything past the building inspectors,, especially with regards to using surface water and outhouses. I would also suggest installing the wood gasification outdoor boiler for DHW now so that you get used to it (instead of changing over to it in a few years). Most people say "I'll upgrade in a few years and then 20 years go by and when they finally do it they say "why didn't I do this years ago?". That's just human nature.

    1. moe_wilensky | | #19

      Yup, everything is legit. Seemed like the best option under the circumstances. I’m keeping my eyes out for a decent used wood gasification boiler but I’m in no rush, got enough on the go. Also, pretty shocked the Nelson building inspector cared about your composting toilet, was this in a commercial setting?

  7. Expert Member
    DCcontrarian | | #14

    My understanding of how bacteria act is that you can never have untreated water in contact with treated water. So if you're not running the UV continuously you'd have to have the system drain when it goes off, otherwise there's no way of keeping untreated water from coming into contact with treated water.

    Have you thought about chlorination? That at least gives persistent protection.

    1. Expert Member
      MALCOLM TAYLOR | | #15


      UV, chlorination and filtration aren't really interchangeable. They all deal with different potential problems. You can only really choose the appropriate treatment by knowing what you are trying to eliminate.

  8. user-1020940 | | #17

    This might give some guidance:

  9. moe_wilensky | | #20

    Well, if after getting the water tested and identifying that UV is sufficient to make the water safe, performing a LCCA on a well vs treatment and getting liability insurance, it looks like there is an at least one option:

    1. moe_wilensky | | #21

      (Bit spendy though)

    2. Expert Member
      DCcontrarian | | #22

      In the specs it says it's not effective against cysts. I would be concerned about giardia.

  10. rockies63 | | #23

    Nope, it was just a single composting toilet in a rural, off grid cabin. The building department in Nelson said "no way".

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