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May 142012

A simple but impressive rainwater collection system.

A person can survive on much less than a gallon of water a day in an emergency (the actual amount depends on things like the type of food you might be eating, the work you are doing, the temperature and humidity of your environment, and your height, weight and age).

But a common rule of thumb is that in an adverse situation, you should plan on about 1 gallon of water, per person, per day.  This keeps you from being dehydrated, and gives you extra water to cook in, and even some to brush your teeth with, too.

But you don’t get any to flush with.  Even modern low flow toilets use 1.6 gallons every time you flush.

The real-world amount of water we actually use in our comfortable lives every day is much greater than the essential need for several pints to keep dehydration at bay.  In addition to toilet flushing, there is dish washing, clothes washing, showers and baths, car washing, garden watering, and who knows what else.  Estimates vary enormously, and there are doubtless regional variations, but it seems the average American uses between 50 – 100 gallons of fresh water every day.

In a Level 1 event, you are going to want to ‘hunker down’ at home for as much as a week (much more than that and you’re moving into Level 2 territory).  The chances are high that you’ll have water, the same as always.  But that is far from guaranteed.  Maybe you have experienced an earthquake that has broken the water mains, for example.  Or a major power outage that means no electricity to drive the water pumps that send the water to your faucets.

Part of the hope in a Level 1 event is that you can continue to live a reasonably normal life during the short-term nature of the event, and due to the event’s anticipated short-term, you choose to stock enough essentials to ensure as much of your comfort as you wish.

So what should you do about water?  And, if you’re going to store some, how should you do so?

It seems to be prudent to keep at least enough water to allow for the essential ingredients of life to continue – maybe a gallon per person per day for essential uses, and some more for not quite so essential uses such as toilet flushing and at least sponge baths.  (Do we need to remind you of the old saying ‘If its yellow, let it mellow; if its brown, flush it down’?)

So maybe you decide you want to have 10 gallons, per person, per day, and maybe you want to be sure to have a ten day supply for three people.  That’s quite a lot of water – 300 gallons.  To look at it another way, that’s over a ton of water, and with the weight of the containers that hold it, you’re probably up to a ton and a half.  (Water weighs 8.35lb per US gallon.)

One more perspective on this 300 gallon supply.  If you’ve been saving up 2 liter drink bottles to keep water in, you’ll need 568 bottles to hold 300 gallons (there are 3.785 liters in a US gallon of water).

Well, don’t let us stop you from buying plenty of 2 liter bottles of Coke, and some industrial grade shelving to stack and stock your water supplies on.  But there’s one source of water, and one easy way of storing it, that most people overlook.


If you live in a dwelling with a roof (ie not in an apartment complex) your house or condo’s roof can be a great rainwater collector.  Best of all, most of what you need is already there; you don’t need to make many modifications at all to be able to get the rain from the roof and into storage.

To encourage you some more, here’s an interesting statistic.  For every 1,000 sq ft of roof area, your roof will collect 623 gallons of water from each inch of rainfall.  Or, to put it another way, with three people each wishing for 10 gallons of water a day, you need a daily average of only 1/20th of an inch of rain.  Well, actually, that wouldn’t work, because 1/20th of an inch of rain would just wet the roof rather than run off it to be collected, but you get the point, I’m sure.

Better to say that if you had 1/2 an inch of rain fall once every ten days, each 300 sq ft of roof would supply enough water for one person.

Okay, point taken.  If you live somewhere wet (like Seattle!) then here’s one of the good sides to this – even the driest month of July still sees 0.79″ of rain, and apart from August at 0.97″, all the other months are way over an inch of rainfall.  But you probably know that, ‘unscientifically’, just from living here, don’t you!

How to Collect Rainwater

This is dead simple.  Although you can do more complicated things, all you need to do is put a rainwater barrel in your downspouts.  There are a couple of things you can do to make this more useful, however.

The first thing is that you want to have your barrels up as high as possible, so you can gravity feed the water on from the barrel to where you’ll be using it, and the more the height differential, the more the pressure from the water in the barrel down to wherever the water eventually comes out of a tap.

From the point of view of the rain coming off the roof, it makes no difference at all if the barrel is immediately under the eaves, or sunk into the ground.

Don’t put the barrel ridiculously high up, though, because you’re going to need some way to get water out of the barrel as and when needed.  The simplest consideration involves two things.  First, you want to be able to reach a tap on the bottom of the barrel.  Second, you want to be able to run a hose from the tap, through a window, and into your house, with hopefully the hose able to run downhill all the way, even if only on a gentle slope.

You also don’t want to get too carried away with scaffolding to support barrels way up the side of your house, and maybe some of the people in your family won’t think they’re the most appealing of ornaments either.

So work out whatever you can as best you can.  Chances are you have several downspouts around the perimeter of your house, you’ll want to do this at as many of them as you feel motivated to tackle.

This water is also great for the garden too, and if you have a fair amount of collection capacity, it might be useful to use it for gardening, in dry months, especially if your local water authority adds any sort of restrictions or surcharges on ‘excessive’ water use.

Water Barrels

You can collect water in anything you like that is reasonably big, which doesn’t leak too much, and which doesn’t add nasty flavors or chemicals to the water.

Most people will choose plastic food grade type barrels.  These can be purchased new (of course) and sometimes used – they are recycled barrels that held some sort of food product or chemical, and which the supplier may or may not promise to have fully cleaned, although often you’ll see that in one point they talk about ‘triple cleaning’ the barrels, and at another point, they also recommend against using them for storing drinking water.

For non-drinking water purposes, used barrels are fine.  But for drinking water, and unless you want to have to either accept some strange flavors or treat/purify the water, it is probably best to get brand new barrels.

Some people will quite rightly avoid plastic entirely, and have the budget to spring for stainless steel.  Others might use galvanized iron, or even wood (probably not a good idea – don’t let wood dry out too much or else it will shrink and the barrel becomes less water-tight).  Fiberglass works.  Glass is great, but sadly impractical.  You can even make water barrels (more like tanks, really) from concrete if you’re wanting something huge in size.

Whatever type of container you get, it is wise to thoroughly rinse and sanitize it (them) before putting water in them.

Choose an opaque color.  Sunlight is as bad for water storage as it is for anything/everything else, so try and keep the water dark (and ideally cool, too, but that might be asking for a bit much).

As for the size of the barrel, there’s no right or wrong answer to that.  Well, clearly there are upper and lower limits – below a certain size and it isn’t worth the bother, and above a certain size and you’ll never fill it.  If you’re looking at typical sized 30 – 55 gallon drum, you will probably end up with close on your target 300 gallons of water, all stored ‘automatically’ for you outside.

A 55 gallon plastic drum, full of water, will probably weigh about 470 lbs – plus the weight of the structure it is mounted on, of course. A 30 gallon drum would be more like 260 lbs.  Both are way too heavy to ever carry, but the 30 gal drum has the benefit of not needing quite as strong a support structure.

Plastic water barrels will cost you anywhere from less than 50c to more than $2 per gallon of storage capacity, depending on the type, their fittings, and where you source them from.

Multiple Barrels Per Downspout

If you wanted to, you could also put multiple barrels, side by side, at each collection point.  Simply run a pipe between the bottom/lower side of one barrel to the same place on the other barrel.  The two barrels will fill evenly and subsequently empty evenly, too.

Alternatively, you could stack one above the other.  If the bottom barrel can be sealed, you simply run a pipe from the bottom of the top barrel to the top of the second barrel, and you take your water out of the double barrel from a pipe at the bottom of the lower barrel.

If the second barrel is not watertight, you’d want the connector to go from the overflow point on the top barrel down to anywhere on the bottom barrel, and you’d then need two points to take the water out from – the bottom of the top barrel and the bottom of the second barrel.  Maybe the lower barrel is below the window or whatever, and you designate this as your ’emergency spare’ and also for garden water, whereas the top barrel with the more convenient water flow is for your main indoor needs.

Connecting Your Barrel to Your Downspouting

This is easy.  Cut and divert your downspouting so that the water pours into the top of your barrel.  Arrange a generous sized overflow tube, also at the top of the barrel to allow overflow water, after the barrel is full, to then go back into the rest of your downspouting.

Be careful that the water coming into the barrel doesn’t just go straight into the overflow exit pipe.

At the bottom of the barrel, you’ll want to fit (or have fitted for you) a regular outdoor tap with a thread for regular hose, so you can then take the water from the barrel, probably via a regular hose, and into the house (or wherever else you want to use it).

Modify as needed if you are having two or more barrels linked together.

Linking Your Barrels Together

This is a great idea.  Maybe you have four downspouts, and a barrel at each one.  Rather than have four hoses all leading into your house, you could instead link the four barrels together and just have one hose, from whichever is the most convenient barrel, to feed into your house.

Simply run a hose from the bottom of each barrel to the bottom of each other barrel.  The hose can even go down to ground level before going up again to the next barrel, it doesn’t really matter, because the rate of water flow through these balancing/transfer hoses can be reasonably low.

For this to work it is important that the barrels be at close to the same height off the ground.  You are making use of the magical property of water to settle at the same level, even if in multiple barrels in multiple locations.  You can easily test the relative heights just by filling all the barrels with about an inch or two of water (so they don’t get too heavy).  You should see the same amount of water in each barrel.  If one has more water in it than the others, you need to raise it however many inches to balance it to the others.

Is Rainwater from the Roof Safe to Drink

Many people enjoy long and healthy lives drinking untreated rainwater from their roofs.

Indeed, when the writer was a child, he lived for some years in a town where his parent’s house relied exclusively on rainwater.  The roof was made from painted corrugated iron, and the water tanks were of galvanized iron.  He remembers as a little boy playing with the tanks, and never thinking to question the dirt in the gutters that the rainwater passed through, or all the slime and sludge in the bottom of the tanks.

Birds would fly overhead and do what they do, and who knows what else happened to the water as well.  It was not treated in any way; it just went straight from the roof to the holding tanks, and from them to the taps inside (this was well before people started drinking bottled water – 100% of all our water came from the tanks).

There are some common sense issues to consider, however.  Try and keep your water away from zinc (such as sometimes used to reduce moss growth), from lead (in paint or flashings), and from treated timbers.  Any sort of new roof should be treated warily before it has had plenty of rain rinse it off.  You don’t want any overflow or discharge pipes from hot water tanks or a/c units to drain onto the roof and potentially into your water tanks.

Screening the tanks can help prevent large (and small) insects and animals get into your tanks.

If you’re in a polluted area, you have a bit more reason to be validly concerned.  All that pollution up in the air slowly settles down, and some of it lands on your roof.  Rain then washes it into your water tanks.

One rule of thumb is that if the water looks clean, smells clean and tastes clean, it is probably fine to drink, especially for a limited period of time.  But if you are concerned about pollution being washed into the water, or just don’t like the thought of drinking water from your dirty roof, by all means filter and treat the water before drinking it.  Or use your outdoor water for non-drinking purposes (cleaning and toilet flushing) and supplement it with the gallon per day of water you feel to be better for drinking purposes.

One plus about rainwater.  Depending on how you might choose to treat/purify it (sometime it would be great to understand how adding chemicals to water is considered to be purification!), you’ll be getting water with no fluoride added to it, no chlorine, and no other nasty chemicals that may or may not have harmful side effects.

Rainwater is generally ‘soft’ rather than ‘hard’.

How Much Water Should You Store

This very essential aspect to do with planning a rainwater system deserves its own page.  And so it now has one – please see How to Calculate How Much Rainwater You Should Store for a mind-numbingly thorough discussion on this point.

 How Long Can You Store Water?

This might seem like a strange question.  Water is just water, right?  H2O.  What can go ‘stale’ with water?

Well, yes, in a perfect world, that is true.  But inevitably, you get biological contamination, and also some other contamination that might become food for the biological contamination.  Add some sun and some nice warm conditions, and even clean pure water will eventually end up with algae and other types of biological contamination.

As the water falls through the air, it picks up contaminants.  It picks up more as it runs over the roof and into your storage.  So rainwater can be somewhat biologically active to start with.

Furthermore, there is always the danger of chemicals leaching out of plastic storage containers and into the water.  This happens slowly over time, so the longer water stays in the same plastic container (and the warmer the temperature and the more the sun) the more leaching will occur.  Smaller containers have a greater surface area to volume ratio, and so need to be emptied and refilled more frequently than larger containers.

Some people recommend changing any stored water once a year.  Others say they’ve had no problems with ‘old’ water many years old.

For ourselves, the nice thing about rainwater is that (depending on your rainfall, storage capacity, and usage patterns) you’re probably turning over the water in your tanks more than once a year anyway.  We definitely renew the plastic bottled water we have indoors every year or so, but the outside water, as long as it is being sort of renewed – either just by surplus rainwater overflowing out of the barrels, or from garden watering and refilling – we don’t worry about, especially if it is water that isn’t our prime drinking water to start with.

Maintaining the Barrels

There’s not a lot that you need to do to maintain the barrels.  Check for leaks, especially around the taps.  Maybe once every five or so years, if you see visible accumulations of algae and sludge in the barrels, clean them out.

An easy way of cleaning the barrels is to use a siphon and just move the end of the siphon tube that is in the tank around to suck up the stuff from the bottom of the barrel.  You won’t need to completely empty the barrel that way.

Needless to say, such activities are best done at a time when rain is forecast in the foreseeable future so as to be able to replenish your water stocks (but there’s no need to do it in the middle of the downpour!).

Legal Issues

Alas, in some jurisdictions, the water that falls on your roof of your house, on your property, may not belong to you!  Anxious environmentalists may be concerned that you are diverting the water from its ‘normal’ path to wherever it would otherwise go (let’s ignore than a house and roof creates an un-normal water collecting/concentrating point to start with, shall we….).

In other states with water shortages and complex water rights, it has been argued that by collecting the rainwater, you are stopping it from mysteriously migrating on to the state’s water supply, and therefore, you are depriving the owners of the water rights of their water (this is definitely the case in Colorado).

The simple act of building structures to hold water barrels may require building permits too.


Adding a water collection facility to your roof’s downspouting can be an easy project you can do yourself, and will provide you with a store of extra water, either for personal use in a Level 1 emergency, or simply to water your garden with and place less stress on the town water system.

There is one difficult paradox – the months when you most need water are the months when it rains the least.  This means that you’ll need to have somewhat larger storage capacity (from the wet months) to carry you through the dry months.


David Spero[suffusion-the-author display='description']

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