Filtering rainwater

[Kelpie]

We regularly collect rainwater from the top of our rigid solar panel bimini. It works pretty well, but we don't put it in the main tanks, instead we fill up jerry cans and various other containers. In the past we've had problems with algae growing in these containers, although they are stored on deck which must be part of the problem.
We've recently added a basic filter in the downpipe, and combined with occasional bleach dosing, the algae problem seems to be solved. We still only use this water for filling the solar shower.

I'm wondering if we're being a bit paranoid not putting this water in the main tanks. We've added a carbon filter for the galley tap which adds another layer of protection.

All of that is a long winded way of saying... what sort of filtration should I use for rainwater going in to the tank? Is carbon necessary? What micron rating? With almost zero head, will I be able to get a decent flow rate?

 

[Gsailor]

Activated carbon filter is good.

Can you add a UV lamp somewhere? I know that is used in the food industry. The wattage needed should be available on via the seller.

I don’t think one can be too careful with what they consume, especially when stuck on your own on a boat.

Good luck.

 

[thinwater]

Before you just start "filtering," you need to understand what it is you are trying to accomplish. For example, the typical granulated carbon filter only makes the water LESS safe to drink (they grow bugs unless the water is chlorinated, and should NOT generally be installed on a boat).

I used this rainwater filter for a year, with the water going right into the drinking water tank.

rainwater filter. It's 1 micron and will flow more than 5 gpm. It is also washable and can be sanitized by leaving in the sun. I developed this idea for a friend with a boat on a mooring, and then started using it myself (catamaran with a hard top).

Then you treat the tank. Chlorine to kill bugs and oxidize off tastes, and a carbon block filter (less than 0.5 micron) to remove cysts (which resist chlorine) and to remove the chlorine (the thing that carbon is best at).

This is basically the way city water is treated. Filter, chlorinate, filter for cysts, and dechlorinate.

basic water treatment

A UV lamp is only going to treat what is sees (not the pipes or far end), they use power, they require regular cleaning, and they have a warm-up period, a factor if they are in-line. Not generally viable.

A strainer on the vent is also a smart idea. Bugs will crawl in, looking for moisture. It's in the plumbing code. I get bugs in my vent filter every year.

 

[Gsailor]

Post 3 seems pretty comprehensive.

I have read that pavements are cleaner than carpets because the rain washes pavements clean, but vacuum cleaners still allow some dirt to lie beneath the surface of the carpet (certainly made me think twice about our house and carpets when I read it) so I am saying rainwater is clean - what it is collected in is important therefore - if only using for showering perhaps less important than if drinking it.

If solar panel from which the water runs off had bird droppings on it - not good.

I do wonder why your Jerry cans are growing algae inside after collecting rain water off a clean solar panel.

Needs a scientist to explain that one - would be interested to learn about algae and what it is and what it needs for growth.

Blue water sailors carry fresh water in Jerry cans tied to the rails BUT the cans are of a certain colour - I can’t remember the colour and whether it was clear-ish to allow sunlight to enter (and also warmth from infra red radiation) and perhaps also uv radiation or opaque to stop sunlight getting in.

 

[GHB]

Been drinking rainwater for years without any problems, radar picks up the squalls so some notice the get the shampoo out and a bucket under the gooseneck with a reef in to guide the rain off the main. Off the awning as well. Always thought it would be cleaner than tap water most places.
But then I'd drink anything until recently

 

[AntarcticPilot]

Post 3 seems pretty comprehensive.

I have read that pavements are cleaner than carpets because the rain washes pavements clean, but vacuum cleaners still allow some dirt to lie beneath the surface of the carpet (certainly made me think twice about our house and carpets when I read it) so I am saying rainwater is clean - what it is collected in is important therefore - if only using for showering perhaps less important than if drinking it.

If solar panel from which the water runs off had bird droppings on it - not good.

I do wonder why your Jerry cans are growing algae inside after collecting rain water off a clean solar panel.

Needs a scientist to explain that one - would be interested to learn about algae and what it is and what it needs for growth.

Blue water sailors carry fresh water in Jerry cans tied to the rails BUT the cans are of a certain colour - I can’t remember the colour and whether it was clear-ish to allow sunlight to enter (and also warmth from infra red radiation) and perhaps also uv radiation or opaque to stop sunlight getting in.

Algae are plants, so they require sunlight, air and some nutrients. They grow from microscopic spores so it's almost impossible to stop them getting in. There will be enough air dissolved in the water to sustain growth; the nutrient requirements are very low.. The thing you can control is sunlight. Without it, algae can't grow - that's why our boats grow a beard around the waterline, but (generally!) much less lower down. So opaque containers should be used to store water, and these should be sterilized with (for example) bleach or Milton before filling.

 

[Sandy]

As long as you boil before drinking, come to think of it 99.99% of the water drunk onboard is made into tea or coffee, then you will be safe.

Why add it to a tank?

 

[emmalina]

I just put it straight in the tanks with a 10 micron filter for general use and a filter block with carbon resin and charcoal + 1 micron filter for drinking. The algae only grows if its left in sunlight

 

[NormanS]

It all seems a long way from the days when the CCC Sailing Directions used to say, "water at burns".
Is it not the case that we're all far too meticulously clean, and as a result, have lost our natural immunity to bugs?
We occasionally collect rain water from the deck, obviously waiting until any visible dirt has been flushed away, letting it go straight into the tanks. As has been said, very little raw water is consumed.

 

[Kelpie]

It's a bit of a myth that rainwater is inherently pure and clean. If you've ever sailed in the south of Spain when the wind is blowing Saraha dust your way, you'll know about it. Awful stuff.

One of the reasons I am trying to aim for a good level of purity is that I am also adding a low capacity watermaker in to the system. I will need good quality fresh water to flush out with each cycle. If I can trust the tank water then it makes things a bit simpler. Otherwise I will need to set up a dedicated flushing container.

 

[Kelpie]

Before you just start "filtering," you need to understand what it is you are trying to accomplish. For example, the typical granulated carbon filter only makes the water LESS safe to drink (they grow bugs unless the water is chlorinated, and should NOT generally be installed on a boat).

That's a good point, thanks. I do have a carbon filter already installed, but it's immediately before the galley tap.

I used this rainwater filter for a year, with the water going right into the drinking water tank.

rainwater filter. It's 1 micron and will flow more than 5 gpm. It is also washable and can be sanitized by leaving in the sun. I developed this idea for a friend with a boat on a mooring, and then started using it myself (catamaran with a hard top).

Funnily enough, I already have a filter built to this design, I didn't realise what I had until now! I got it off someone in exchange for a few beers. Mine is fixed directly under the runoff pipe from my solar panels. Perhaps a coarser filter first would be better but it's fairly neat the way it is.
I'll need to get some spare filter socks for mine. The lip around the existing one has broken down (UV?) and it's slid down inside the pipe. Still works though.
Since I installed this filter a few weeks ago, I've not had any more algae in my cans. So perhaps I already have what I need

Then you treat the tank. Chlorine to kill bugs and oxidize off tastes, and a carbon block filter (less than 0.5 micron) to remove cysts (which resist chlorine) and to remove the chlorine (the thing that carbon is best at).

That might take some finding. I can get 5 micron carbon filters, and 5 or 20 micron sediment filters.
What kind of flow rate can I get through a 0.5 micron filter?

With the addition of a watermaker, I'm hoping to move away from needing to use chlorine in the tanks, because then I end up in the situation where I cannot use tank water for flushing. But maybe I should just accept that chloride is necessary, and keep back some product water for the flush.

 

[geem]

It's amazing how much dirt is in rainwater. We used to collect a lot off our sun cover. In a tropical downpour we once collected 500 litres in 2 hours.
We have 1 inch down pipes that go into our tank via a 10" filter housing. The filter housing has a 1 micron filter. The clear filter housing is pretty handy as you can see how dirty the filter is getting. It really doesn't take that long for dirt to start appearing on the filter media.
We also use another 1 micron filter in a clear housing on the discharge from the tank, just after the pump. Immediately after this is a carbon filter. We can drink from any outlet in the boat.
We don't chlorinate the tank unless the boat has been laid up for a few months. Living aboard, the turn over rate in the tank is high. We use about 60 litres per day and keep about 300-400 litres in the tank.
Watermaker is passed through a UV filter before it gets to the tank

 

[Dantp]

We get growth in jerry cans regardless of whether they are tap filled or rain water. But only if we leave them in the sun.
We just use a bit of cloth in a funnel if the rain is clean (eg Ireland), or a 10" inline filter with 5 microns if we are getting more suspect water. We will also pre treat suspect water with chlorine.
Thinwaters water filter in post 3 looks like a really good solution.

 

[Slowboat35]

What's the big deal with filters? Any bits will sink to the bottom so son't use the dregs, just like a fuel tank.

All that's needed is a couple of steritabs and don't store the cans in sunlight (A tarp maybe?). How hard is that?

 

[Kelpie]

What's the big deal with filters? Any bits will sink to the bottom so son't use the dregs, just like a fuel tank.

All that's needed is a couple of steritabs and don't store the cans in sunlight (A tarp maybe?). How hard is that?

The tanks are almost brand new and have never had any bad water in them. I'm a bit precious about them and want to keep them clean. Maybe I'm being over cautious?

 

[thinwater]

If you want to learn about drinking rainwater, Google municipal sites in Australia and some of the US southwest. Also some islands. It's all they have, so it has been extensively studied by public health authorities.

Keeping the hard top clean when cruising full time is pretty easy. Birds don't hang out and the sun and rain do most of the work. Also, white gel coat takes much better advantage of the sun for sanitizing than most roofing materials.

Texas study on roof types. Lots of data. http://www.harvestingrainwater.com/...-Quality-for-Rainwater-Harvesting-Systems.pdf

Rain Tanks in Sydney. http://epress.lib.uts.edu.au/research/bitstream/handle/10453/18312/2010004037.pdf?sequence=1

Regulations. http://www.rainwaterharvesting.org/policy/legislation_international.htm

CDC info page. http://www.cdc.gov/healthywater/drinking/private/rainwater-collection.html

DIY in NC. http://www.motherearthnews.com/diy/home-garden/harvesting-rainwater-zm0z13jjzhun.aspx

Texas health video. Very good common sense approach. http://www.screencast.com/t/5ICkbUIzmcl, http://rainwaterharvesting.tamu.edu/in-home-use-videos/

Text version. http://rainwaterharvesting.tamu.edu/files/2011/05/gi-366_2021994.pdf

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No, it is not sterile. But most of the pathogens you need to worry about come from other people, not nature. Atmospheric pollution can be an issue in some places, but you have to address that on a local basis.

 

[geem]

What's the big deal with filters? Any bits will sink to the bottom so son't use the dregs, just like a fuel tank.

All that's needed is a couple of steritabs and don't store the cans in sunlight (A tarp maybe?). How hard is that?

Sediment in water is easily stirred up by boat motion unless you just sit in a marina. It's so much better to not have sediment in the tank. Try sticking a cheap camera endoscope into your tank and having a look what's in there. It might change your opinion on filtration

 

[thinwater]

Sediment in water is easily stirred up by boat motion unless you just sit in a marina. It's so much better to not have sediment in the tank. Try sticking a cheap camera endoscope into your tank and having a look what's in there. It might change your opinion on filtration

Additionally, you cannot sanitize a tank with bleach if there is sediment. The bleach will not penetrate.

Most simply, it is quite easy to filter the rainwater with a 1 micron bag before it reaches the tank. Much easier than cleaning the tank. Also good for marina taps that shed rust and algae. This filter was intentionally based on an industry standard bag, for economy and because they are widely available, just not at the hardware store.

1 micron is pretty fine, so not a lot gets past it, yet flow is still high.
rainwater bag filter, 1 micron.

 

[geem]

1 micron is pretty fine, so not a lot gets past it, yet flow is still high.
rainwater bag filter, 1 micron.
[/QUOTE]
Yes, we run a pair of 1" pipes from the sun cover into a tee then into a standard 10" filter housing and 1 micron filter. It always surprises me that with the pipes running full bore, the filter happily passes the water without a problem

 

[FulmarJeddo]

We have an off grid holiday home and have always used rain water for washing, washing up etc, but until last year we loaded the car with containers of drinking water from home. After a week of the family visiting we were running very short of drinking water. I did a bit of research and found British Berkefeld Filters They sounded good, so bought an 8.5L version. We have now spent two extended summers drinking filtered rain water. It tastes better than chlorinated water with no ill effects. Our rainwater is stored underground, so keeps fairly cool, but often comes out of the tap with a brownish tint. We have to wash the slime off the outside of the filters every couple of weeks to keep them flowing. We keep the header tank topped up and have a constant supply of fresh drinking water. Just storing a small quantity of filtered water means it doesn’t go off. It’s obviously not suitable to carry a stainless water filter on a boat, boat it wouldn’t be too difficult to adapt the idea with a header tank with the candle filters dripping into a storage tank.