Wednesday, June 16, 2010

DIY rainwater

However did the majority of Australian urban dwellers become so dependent on mains water? In the not so distant past, water self-sufficiency was the norm, and it still is in rural areas. It really is not so difficult to harvest enough rainwater to be self-sufficient in terms of household use. Sure, tanks are expensive, but it doesn't cost all that much more to be water self-sufficient than it does to, for example, have a tank plumbed to just the toilet, or to install a tank and pump for garden usage. Even though a full-scale system will cost more initially, it will be more cost-effective, and it will "pay for itself" more quickly (partly due to the various associated savings mentioned later in this post).

Admittedly, house blocks are getting smaller and houses are getting bigger, but there is often some way around a perceived lack of space for water tanks. There might not be much space adjacent to your downpipes, but you can perhaps install small slimline (or even ultra-slim) tanks along your wall as collect-and-feed tanks and have a large storage tank in the back corner of the yard. (Connect the bases of all the tanks together and the water will level out and automatically fill the storage tank.) Slimline tanks might be fairly useless as water storage tanks, but they can collect and transfer enormous quantities of water to a large storage tank.

Since rainwater tanks are expensive, if you are thinking of investing in one (or more), it would be a good idea to "get it right" from the outset and maximize the benefits of making that investment...rather than going through the same learning curve I went through!

Mistake No. 1: My biggest mistake was to install a 5,000L tank to use for watering my garden. Actually, an awful lot of people do that, even those, like me, who live in the sort of climate that has plenty of rain in winter (so we don't need to water the garden then) but has next to no rain in summer. So what happens? The tank fills up quickly at the start of winter and, for the rest of winter, all further rain just runs down the stormwater drain. Then, when summer arrives and the garden needs regular watering, the tank runs dry after watering the garden for a few weeks, then the tank sits empty for the rest of summer.

5,000L tank

Assuming you are paying somewhere between $1 and $2 per 1,000L for mains water, that tank will save you about $10 per year....and the tank cost what? $1,000? Rather a poor investment I'd say, and not a lot of benefit to the environment either. But...rainwater tanks can be a very good idea. You just have to do it right!

Tip 1:
Think about your local weather patterns and about what you will use the rainwater for. My 5,000L tank might have been sensible somewhere like Sydney, which has a reasonable proportion of its rainfall in summer, but in locations with dry summers, buying a tank to water the garden is a waste of money.

If you have lots of rain in winter, why not use the rainwater during winter while there is plenty more coming to replace what you have used? We all use water inside the house all year round. If your tank is plumbed to your house, it will in effect be emptied and refilled something like 5 times over the course of winter. This means that your investment in a 5,000L tank will give you something like 25,000L of water.

Mistake No. 2: My original tank was fed by only one downpipe. So, if we did happen to have a summer thunderstorm with a heavy downpour (this was 8 years ago so I don't remember if we did), 3/4 of the rain landing on my roof went down the stormwater drain instead of into my tank.

Tip 2:
To maximize the amount of water you can collect, regardless of what tank capacity you have, ensure that every drop that lands on your roof goes to your tank(s). To do this you will almost definitely need more than one tank. However, if you connect them together at their bases, they will function as one tank, filling and emptying in tandem. This means that your plumbing between the tank outlet and the house/garden need only be connected to one of the tanks.

Mistake No. 3: When I decided to use my rainwater in the house rather than the garden, I had no idea how much water I would need in the house to last all summer without rain, or how much water would be available for collection (how much rain would land on my roof). I suppose I thought that it didn't matter much if we ran short of rainwater because we could always switch back to mains water until the next rain, so I just went with the idea that we needed a bigger tank, and that we needed to collect the water from all the downpipes. I bought a 9,000L tank and installed it at a different downpipe.

9,000L tank ( I had to move the fence and gate to fit this one in!)

I also bought a 1,000L modular tank to fit in the small space at the other side of the house, and redirected the other two downpipes into that tank.

1,000L collect-and-feed tank

We used that setup for a couple of years, and despite just being guesswork, that gave us roughly the right capacity in terms of having enough rainwater to use for everything inside the house all year round. (That is, 10,000L for two people in a dry-all-summer climate.) One year we did not run out of rainwater at all, and the other year we had to switch back to mains water for only a couple of weeks. In purely financial terms, that was probably the optimum capacity for us. However, during winter, rain fell faster than we used it, so we still had overflowing tanks for the last half of winter. I couldn't bear the thought of all that good water going down the drain so I bought another tank - a 23,000L one this time - and installed it in the back corner of the yard, and just connected the base of it to the other tanks (no water from the roof runs into it directly).

23,000L tank used just for storage

The above setup has been in use for about 5 years now, and it seems to now be the right total tank capacity given our roof area and local annual rainfall. Some years the tanks don't quite fill completely, and some years there is a little overflow going down the stormwater drain. Also, now that we have water restrictions, it is very convenient to have more rainwater than we need for household use and to be able to use quite a lot of it in the garden. Even so, if I'd known at the outset the optimum total capacity for us, I would have designed the tank layout differently and bought different-sized tanks...a larger tank costs more than a smaller one of course, but not all that much more.

Tip 3:
If you know how much rainwater falls on your roof in an average year and how much water you use for different purposes, you can better plan how you will use the water and work out your optimum tank capacity. Do you just want enough rainwater to flush the toilet and wash the clothes, or enough to plumb it to the entire house? (The plumbing modifications are simpler if it is plumbed to the house as a whole.) Will you be able to collect enough for the garden too? If you want to use your rainwater just in the garden, what tank capacity will you need to see you through the longest dry spell you are likely to have in your locality?

To find out how much water you can collect you will need to know your local annual rainfall and the total area of roof from which you collect rainwater (floor area + eaves + garage/patio/etc). For rainfalls within Australia, go to Climate Data Online and select Rainfall - Monthly - your location. Multiply the roof area (square meters) by the average annual rainfall (mm). The result is the number of litres of rainwater you can collect. If you prefer to use other units of rainfall or area, there is a rainwater calculator you can use here.

According to statistics published in NSW Guidelines for Greywater Reuse in Sewered, Single Household Residential Premise (page 6), the average in-house water usage for a household of three is 603L/day (bathroom 198L, laundry 131L, toilet 124L, taps, including kitchen, 140L), and outside usage (garden, pools, etc) is 223L/day. However, you might be able to get a more accurate idea of your usage by looking at your water bill, particularly if you have "wet" quarters where all your water usage is inside, and "dry" quarters where you also need to water the garden regularly.

Perhaps you can collect 80,000L, for example, over the course of an average year, but remember that you are also using that rainwater throughout that time. To collect and use 80,000L in a year, you might only need a total tank capacity of, say, 20,000L. In general, in order to effectively use any given amount of rainwater, locations that have reasonably regular rain during summer will need much less storage capacity than localities with long dry summers. (You can find your local mean rainfall figures for each month of the year from the Climate Data Online site.)

Unfortunately, even with all the above figures at your fingertips, there is still a degree of guesswork involved in deciding your optimum total tank capacity! It might also help to talk to other householders who have tanks in your area and see what works for them.

Mistake No. 4: When I connected the bases of all my tanks together so that the water level in each tank levels out, I used 19mm hose between the tanks with the intention of allowing a reasonably quick water flow between tanks. However, the 1,000L modular tank came with an ordinary tap (about a 13mm internal bore I suppose). I should have replaced that tap with a larger one, but I didn't. I also used ordinary small-bore taps at the tank that all the others connect to. Water travels more slowly than you might think when gravity is leveling it out!

 All the tanks connect to this one at its base.

Since the 1,000L tank receives rainwater from over half my roof area, it fills much quicker than the other tanks. This is not usually a problem, but during a particularly heavy downpour it fills and starts overflowing even when there's still plenty of space in the other tanks simply because the water does not travel to the other tanks quickly enough.

Tip 4:
When connecting multiple tanks together, ensure your taps and hoses all have an internal diameter of at least 19mm to allow water levels to level out reasonably quickly. This won't be an issue if all your tanks are similar sizes and are fed by similar amounts of your roof area, but that is not likely to be the case.

Mistake No. 5: The overflow spouts on my four tanks are not all level with each other. (This was not a "mistake" exactly - it was simply not possible to have them all level.) This means that one of my tanks reaches overflow point a little before the other tanks, so at that point I need to turn off its tap so that water from the other tanks does not flow back and out the overflow spout of this lowest tank (so the other tanks can also fill completely).

Also, the overflow spout of my 23,000L storage tank is about 60cm higher than any other tank - it is a taller tank and also on higher ground. This is the tank that has no direct input of water from the roof so, even though the leveling out process can fill it up to a point, it obviously can't fill up the top 60cm of the tank. Once all the other tanks are full, I need to turn off the tap at its base and pump water to it from the other tanks to fill it completely (which also makes space for more rain in the other tanks). Fortunately, this is not particularly difficult. Since rainwater is automatically pumped to all my taps (by a pressure pump that kicks in automatically whenever I turn on a tap), including those on the outside of the house, I just connect a rainwater hose to an outside house tap and poke the other end in the overflow spout of the 23,000L tank, and then turn on the outside house tap. The tap on the base of that tank remains closed until sometime next summer. When the other tanks are getting close to being empty, I open the tap to allow the water to level out between all the tanks again.

Tip 5:
If possible, make the overflow spouts on all tanks level with each other to simplify management. If this is not possible, make sure you have taps at each tank (don't connect the tanks together with hoses alone) - otherwise no tank will be able to be filled further than the height of your lowest overflow spout.

Conversely, it makes no differences whether the bottoms of your tanks are level with each other or not. However, make sure that the pump that delivers your rainwater to the house and/or garden is connected to the tank that has the lowest base. That way all the water from your other tanks will end up in the tank you pump from (this will become relevant if you are about to run out of water).

Other tips...

  • If you want to use first-flush diverters and/or leaf catchers, install them when you first install your tanks. This will be much, MUCH easier, and cheaper, than retrofitting them later. Even if you don't want to install these, allow enough vertical space between your gutter outlets and tank inlets to install them later just in case you change your mind!
  • If you are concerned about adverse health effects from bacteria and traffic-generated pollution that might be present in your rainwater, consider installing rainwater filters on your kitchen taps. (I personally would want a filter if we lived in a high-traffic area, but since we don't, we don't use a filter.)
  • You can install the tanks yourself, following the manufacturer's guidelines, but you will need to hire a licensed plumber to plumb the water to your house and to ensure that the mechanism for switching between mains water and rainwater conforms to health regulations.
  • Sustainable Gardening Australia has published a shoppers' guide to rainwater tanks here. This discusses the pros and cons of tanks made of various materials.
  • You will need a pressure pump connected between one of your tanks and the house to give adequate water pressure for showers, etc. This pump will automatically switch on every time you turn on a tap. The pump will not be very noisy, but you will hear it. I found this a little annoying for the first few days, but I soon got used to it. If you think this noise will bother you, take this into account when you decide where to locate your pump. The up side is that you will know if anyone has accidentally left a tap dripping - you'll hear the pump cutting in and out at times when nobody is using water.
  • When deciding what size tank to buy, check that you have suitable access to get the tank from the street to wherever you want to put it. If access is a problem, you might decide to change the location of the tank, buy a different shape/size tank, or hire a crane to lift the tank over whatever is blocking access. Crane hire is expensive, but a large tank plus crane hire can be less than the cost of achieving similar storage capacity using smaller tanks. (I had to hire a crane to move my 23,000L tank into my back yard.)
  • It's a good idea to have a stop cock as the very first fitting attached to each tank. That way, if you need to change a tap (taps do break) or hose, you can turn off the stop cock and not lose any water.
  • These days there is an enormous range of tank shapes and sizes available, so you'll probably be able to find tanks that suit whatever space you have. If you are aiming at collecting and storing large quantities of rainwater, the cheapest option is still the traditional round tall-ish type of tank if you have space for one of these somewhere in your yard. For reference, with the type of poly tanks I used, a 5,000L tank has a diameter of 1.85m (inlet height 2.05m), a 10,000L tank has a diameter of 2.59m (inlet height 2.16m), a 25,000L tank has a diameter of 3.73m (inlet height 2.40m), and a 46,400L one has a diameter of 4.60m (inlet height 2.95m).
Pros and cons of running a house on rainwater... 

Buying tanks, pump, fittings, etc., involves quite high initial costs, and mains water is still incredibly cheap. If expected savings on your water bills are your main motivator and you calculate how many years it will take for your rainwater system to "pay for itself", you'll probably decide to stick with mains water. (Even if you use no mains water at all, you'll still need to pay the sewerage and water supply charge.) It is only when you take into account the other savings associated with rainwater use that it becomes reasonably financially attractive.

The big potential saving - or so I'm told - is that your hot water system will last three times as long if you use rainwater rather than mains water, and your washing machine will also last much longer. (I've not been using rainwater long enough to have proved that for myself.) Not needing to replace those devices will go a long way towards paying off your rainwater system. 

There are also various smaller savings which take effect immediately. You'll need to halve the amount of shampoo and laundry powder you use to avoid being swamped in bubbles. You won't need to use fancy cleaners to remove mineral deposits from your shower (because there won't be any). You will use hand lotions and moisturizers much less than usual because rainwater does not dry your skin the way mains water additives do. One delightful surprise for me was that the dry cracking heels that I suffered from for years stopped being a problem. I didn't actually notice the problem going away (human nature being what it is!), but the year we had to revert to using mains water for a couple of weeks I suddenly started having this problem again (until it rained and we could shower in rainwater again).

On the down side, you'll probably need to clean your toilet a bit more often because rainwater does not contain chlorine. Also, if you are washing greasy dishes you might need a bit more detergent than usual to cut through that grease.

Possibly the main inconvenience of using rainwater is that you need electricity for your pump to operate. If there is a power failure, you won't get any water out of your taps. Of course you can always switch over to mains water until the power comes back on, or collect a jug of water directly from a tank.

Quite apart from the many environmental benefits of using rainwater in the house, and regardless of whether it saves you money or not, I just really like using rainwater. It tastes nice, it does not smell of chlorine, it leaves hair soft and silky, and hot rainwater showers feel pretty good too. Besides, it strikes me as absurd to rely on public utilities to treat and deliver water to me when plenty of perfectly good water lands on my roof. It is even more absurd that our urban areas have concurrent water supply problems and stormwater disposal problems - wouldn't rainwater tanks neatly solve both problems?


  1. nice setting of your water system. this is one of the best set up of water tank will help you in everyday chores.

  2. It’s true that having your own water storage tank can be a big help, especially when it comes to saving on the house bills. However, people should try to get the right size storage tank for their needs. I think the root of the problem was that you didn’t know exactly what size storage tank you needed, and ended up buying a lot of them. Well, the mistakes that you make are life lessons you should learn from, and I think that’s what happened to you!

  3. Yes, precisely! And I figured I'd write about my mistakes so others can learn from my mistakes rather than repeating them. :)

    BTW, I've since realised I made one more mistake. My pump should have a bigger pressure tank so that the pump does not need to switch on every time I turn on a tap. I guess I'll eventually need to replace the pump, so I'll fix that when I need a new pump.