Water Treatment for Off-Grid Tiny Homes

How to Treat Water in an Off-Grid Tiny House

Treating your water in a tiny house or an RV has different challenges than in a sticks and bricks house.

1. Don't have a ton of space for equipment

2. Don't want to spend more than your house cost to build

3. Might not have an unlimited water supply.  We have to manually fill our 45 gallon water tank, so any wasted water is a big deal.

4. Might not have an unlimited power supply.  We run on four solar panels and a battery, so we can't spare any extra power for water treatment.

5. Might be hooked up to a questionable or variable water source.

The good news is that you can treat your water on a small scale using the same methods as household water treatment.  It's not hard, it's doesn't require a huge up-front investment, and the long-term cost of treating your water is almost always lower than not treating it at all.

Choose Your Source Wisely

When we're filling up our tanks, we try to use the best available source.  Common sense rules here.  Treated municipal water, household well water, and campground water is usually OK, and can be made much better with secondary treatment.  The garden hose behind the gas station would not be my first choice, but if I had to use it, I'd definitely treat it.  Surface water (from springs or streams) needs thorough treatment—avoid it if you can, treat it if you can't.  Cloudy purple water out of the swamp next to the power plant?  Find somewhere else to get your water.

If you have no other choice but to use a questionable water source, this method in this article is very effective at making your water safe.  If you just want to make your water quality better, or you've read the news too much to trust municipal water, this method will also address nearly every concern you might have.  If you use this method on every fill, regardless of the source, you'll save some money, and maybe even avoid some health problems.

Pre-Filter If Necessary

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The first thing to check is if your water is cloudy.  Grab some in a clear glass and take a look.  If it's cloudy at first, and then the cloudiness rises to the top and disappears within a minute or two, that's just air.  No need for a pre-filter.  This kind of cloudiness is very common in municipal supplies, especially in the winter.

If the cloudiness hangs around for a while or settles to the bottom, it's probably sediment and water needs to be filtered first.  You can install garden hose fittings on a standard filter housing and use 5 micron sediment filters, which should clear up most sediment issues at the tap.

Soften Your Water

A water softener uses a process called ion exchange to trade positively charged impurities in your water for sodium ions (Na+). The softener removes calcium (Ca2+) and magnesium (Mg2+), a.k.a. "hardness," and replace them with an equivalent amount of sodium. Softeners also remove other positively charged impurities like iron (Fe2+), manganese (Mn2+), and radium (Ra2+).

After a while, your softener will run out of sodium ions to trade, and it will need to be regenerated.  Portable water softeners have a top that opens to allow you to pour in a package of regular table salt.  After a few minutes of rinsing the salt through the tank and flushing it with clean water, the softener is regenerated and ready to treat your water again.

Why is softening water so important?

Softening water prevents the formation of lime scale in the water heater, dishwasher, valves, faucets, and shower heads.  It prevents the formation of soap scum, so soap lathers better and rinses cleaner.  You'll need to use far less soap to do the same job.  And not covering everything in soap scum means your your skin and hair will be softer when you shower with soft water.  Longer life on appliances and fixtures, less waste on household products, no more dry skin -- what's not to love?

I soften all the water that goes into my fresh tank each time I fill up.  I simply attach the softener to the fill hose and fill 'er up.  If it's freezing outside, or if I'm trying to reduce weight, I'll use my blowout plug and my portable 12V air compressor to push the water out of the softener.

Disinfect Your Water

Boiling is the most effective way to disinfect your water.  But it's not practical to boil all of your water all of the time.

I follow the NIH guidelines of 1/8 tsp of bleach per gallon of water with a minimum contact time of 30 minutes.  My fresh tank is 45 gallons, so a full tank needs just under 2 tbsp.  Each of my jerry cans holds 5.5 gallons, so if I'm hauling or storing water, each one needs just under 3/4 tsp.  This not only kills bacteria in the water itself, but keeps the inside of the tanks clean.

This method is very effective at destroying bacteria and viruses, and the longer the chlorine is in contact with the water, the better.  It's a so-so method against protozoa, but we're going to deal with them in the next step.  Incidentally, if your water contains hydrogen sulfide and smells like rotten eggs, this step will fix it.

Filter Your House Water

I don't actually want to drink a bunch of chlorine.  I don't even want to inhale it in the shower.  Even more so, I don't want to drink all the toxic disinfection byproducts that I probably just created by adding all that chlorine to my water.  And I don't want to drink or bathe in nasty chemicals either.

I also don't want to get a protozoan disease from Giardia or Cryptosporidium.  Dysentery does not sound like fun to me.

I can address all of these issues in one step by running all of my water through a high-flow carbon block filter with a 0.5 micron rating.  Carbon filters are great for removing organics like pharmaceuticals, pesticides, or nasty disinfection byproducts like trihalomethane.  They're also good at removing chlorine and lead, which I'd really prefer to take out of the water before I use it.  And because the rating of the filter is smaller than 1 micron, it will also filter out any protozoa that might be hanging out in my water.

A small 10" filter housing after my water pump houses my 0.5 micron carbon block filter cartridge.  Don't forget the mounting bracket and the wrench.

Purify Your Drinking Water

I care a lot more about the purity of the water I put in my body than the water I use to wash the dishes.  Even though I went through several steps to remove potentially nasty contaminants from my water already, I think it's worth one extra step to get rid of pretty much anything else in the water that might bother me.

The usual household water treatment setup would use reverse osmosis to filter drinking water.  That might work well for a tiny house with full hookups, but it doesn't work for my off-grid use.  An RO system produces a lot of waste water, and I can't afford to waste any water.  The prefilters are usually reasonably priced, but the membrane can be expensive, and it'll break if it freezes.  There's also a manifold with lots of tubes that's tough or impossible to winterize.

Instead, I use a deionizer to purify my water.  The ZeroWater dispenser has a five stage filter that includes a carbon step (in case we missed any heavy metals or pharmaceuticals) as well as an ion exchange step that trades anything positively charged (including all that sodium from the softener) for H+, and anything negatively charged for OH-.  Add the two together, H+ plus OH- equals H2O—pure water.

If my deionizer freezes, no big deal.  The cartridge might break, but it's disposable.

Some folks worry that removing all the minerals from your water is bad for you.  Don't worry about me.  As someone living in a first world country, I get plenty of minerals from my diet.  There's salt on my fries.  There's fluoride in my toothpaste.  I had avocado toast for breakfast (copper, potassium), kale for lunch (manganese, copper, calcium, potassium, iron, magnesium), and brussels sprouts for dinner (selenium, copper, zinc, manganese, iron, calcium, potassium, phosphorous).

The fact is, there are often some beneficial minerals in tap water.  And there are some inert ones.  But those impurities ride along with all the nasty stuff I don't want to drink.  There are better ways to get the good minerals without having to drink all the lead and Viagra that your local municipal water delivers.

Want to learn more than you've ever wanted to know about tiny living and off-grid water treatment?  Check out tinywatertreatment.com for a deep dive into the topic.