Progress report on water systems

Here is a brief update on how the water systems I've installed are faring.

Hot water

I have written articles about my hot water systems here and here.

The system was finalised at the beginning of September 2014, and has worked flawlessly since. We have not boosted it through Spring/Summer -- in fact, I have shaded the collectors to stop it boiling. Some things I really like about it:

• I now have shorter "runs" of pipe between the hot water system and where I use the water, which means less waste
• Because water is effectively heated instantaneously within the hot water system tank (discussed in previous articles), it has no taste, and so can be used to make tea and cook with. There is also no concern with Legionnaires' disease.

Rain water

I have written about our rainwater systems here and here.

We have been exclusively using rainwater since the beginning of September. This includes watering the garden, washing clothes and people, toilet flushing. At the beginning of September, we had ~35 kL of stored water of which I estimate about 30 kL is usable (due to the position of the tanks relative to input/output feeds, etc) -- this was not something I previously considered. Because the system was not completed until December, we did not capture the Spring rain maximally, and Spring rains were very sparse this year. It has been a relatively cool and dry Spring.

We have been very frugal with water, and have captured our washing machine grey water, and grey water from the kitchen for use on the garden (we don't keep washing machine grey water if washing nappies). Until last weekend, I estimate that we had used about 23 kL or a bit under 200 L/day.

I (very roughly)  estimate that this water is used as follows:

• 6 - 8 toilet flush/day: 50 - 70 L daily
• 1 load of washing / day: 70 L daily
• kitchen sink: 30 L daily
• garden direct watering: 50 L daily
• bath/showering: 30 L daily

Clearly, the big users are the toilet and the washing machine. 

Toilet

The toilet is a total loss, because that water goes straight to waste. I want to replace one of our flushing toilets with a composting toilet. This will save a lot of water, and also give us more compost.

Washing machine

Most of the washing machine water we use in the garden, though in a sub-optimal way. This probably seems like a lot of washing, but we have two young children, one of whom is in the process of toilet training (ie. we still wash nappies, as well as soiled clothing)

Bath/shower

I generally wash in the shower every 2 - 3 days, and sometimes use the bath after the kids. They have a bath every 2 - 3 days. My wife often showers at work.

Lessons learned

• Some water is easy to save, and grey water represents an easy saving if it displaces fresh water on the garden.
• Timer taps make it easy to waste water on the garden. Also, it is hard to measure how much water is being used. I set up a timer tap out the back on the vegetables and fruit trees (separate circuits). Given the amount of grey water we have, it is almost possible to water all our trees and vegetables with grey water only (note that there are hygiene implications of watering vegetables with grey water -- make sure you do your research if you plan on doing this). In future, I will consider watering more by hand and less by the drippers
• I accidentally let about 5000 L out of the tank via the vegetable drippers. I wanted to give the vegetables a bit of water before a very hot dry day, but forgot to turn them off until the next day. In future, I will never leave a tap running without an auto-off or an alarm to remind me.

Likely outcome for the Summer of 2014/2015

We will probably run out of water this Summer. I think we have about 5000 L (accessible) remaining in the tanks, which will last only about 25 days. I doubt we will get significant rain in that period. (We have had about 15 mm of rain in the last 4 days, which is very unseasonal, and is factored into this estimate). We are in the fortunate position to be able to switch over to town water easily.

Plans and thoughts for Summer 2015/2016

• I would like to have one toilet replaced with a composting toilet by next Summer
• I might add some extra sheeting to the pergola which will increase the rain collection area (very important for catching every drop of Spring rain)
• We now have all the tanks installed and connected, so will maximally collect the Spring rains in 2015
• I will try to do more to keep "dirty" clothes separately in the laundry, and wash them irregularly, keeping them for dirty tasks. This can hopefully ease the washing load

Conclusions

Water is one of those things that requires a whole system to perform well. Any compromises in subsystems will compromise the whole system. We are getting closer to the ideal that I modelled here, at which point I think we will operate (almost) solely on rainwater. I am hopeful that next Summer, even if we don't have a composting toilet, we will go a lot closer. Even this year we might well have made it through summer, had I not accidentally released that water. 

I think this system shows that it is possible to be self-sufficient for water with a relatively small amount of storage, however it does not leave any margin for error. In a fully off-grid scenario, I would want double the storage, even if it was rarely/never used. Of course, in such a scenario space would be less of a premium than it is in an urban environment!

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This article was written by Angus Wallace, and first appeared at guesstimatedapproximations.blogspot.com.au

 

Water at my house - part 1: rainwater

This post will evolve, but the idea is that is summarises what we've done to manage the water at our place. It will contain links to other relevant posts I've written.

Rainwater

Our house was built in the 1950s, and is typical of houses from that era. It is mostly brick, with a tile roof on the main part of the house and a lean-to at the back with corrogated iron. There are four downpipes on the house, one in each corner. Those on the Northern side of the house drained to the back yard. The downpipe at the South-East corner drained to the street (that has possibly the largest flow of the four), and the pipe at the South-West drained to the neighbour's  front yard!
At the back, our garage had a gutter down the East and West side.

Some considerations for our rain water system:

• We wanted to catch all the water that fell on our roofs, and not waste any
• We didn't want big tanks in the front yard
• We wanted to use the rainwater in the house
• Where possible, we wanted to avoid pumping the water (gravity feed) (in keeping with low energy, as described in these posts)

Rainwater plan

Below is a schematic for our rainwater system

Figure 1: Schematic (not to scale) of the water systems as installed

We decided to install 5 rainwater tanks. We installed

• 2 x 15 kL tanks in the NE corner of the block as bulk storage.
• 1 x 5 kL tank near the pergola
• 2 x 1 kL tanks at the front of the house

I have performed a detailed analysis (using historical meteorological data) of whether this will be sufficient rainwater storage in this article.

This leaves one downpipe without a tank attached in the NE corner of the house. For now, I've raised the pop (within the gutter), so that the water will preferentially drain to the West (the other downpipe that's being caught by the 5 kL tank) and will only go down the NE downpipe if the rain is exceptionally heavy and the gutter is in danger of overflowing (refer to Figure 2(a) for detail). I plan eventually to run a new gutter around the house-attached pergola on the northern side.

Figure 2: (a) cross-section of a gutter showing the raised pop that will only drain when the gutter is in danger of overflowing. (b) detail of the manner of connection of the main solar hot water system

The five rainwater tanks equilibrate via blue-line poly pipe. The 5 kL and 15 kL tanks are connected by 25 mm blue-line. This is low-pressure, and I've also included a gravity fed tap in the middle of the vegetable patch to allow gravity fed watering. The two 1 kL tanks are connected to the 15 kL tanks via 40 mm blue-line. Because of the front tanks' small capacity and distance to the rear tanks, I wanted to avoid a situation where heavy rain caused them to overflow despite there being storage space at the rear tanks. The larger diameter of the 40 mm blueline allows water to more-quickly move from the front to the back of the house.

The 25 mm blue-line from the 5 kL tank is connected to a Grundfos variable speed pump which supplies the house. To use this, we also installed a valve that allows us to turn off the water supply near the street. To save energy, we run our pump at a lower pressure than the main supply (~25 psi, versus 55 psi for the supply). I think that this makes our plumbing work better (our shower in particular works better at lower pressure).

System advantages

1. Because the tanks are in equilibrium, and are scattered, we have low-pressure rainwater available around the yard. This is a very simple system, and lets us access water under its own pressure without using a pump. Simple, non-powered systems are cheap and resilient, as described in these posts.
2. Little/no rainwater is wasted. It would have been possible to create a wet sump system, whereby the stormwater from the front of the house was routed to the tanks at the back underground. This would have allowed us to avoid having tanks in the front yard. The problem with this system is that any water left in the pipe between rains tends to go bad. To avoid this bad water entering the rainwater tanks, this needs to be drained. Apart from being a waste, it is very difficult on our block which is almost flat. Although there is water inside the blue-line pipe, this water is often moving: as we use water in the house, it causes all the tanks to re-equilibrate, which cycles water through the pipe and prevents it going bad. It would not have been possible to adjust our gutters to direct water out the back without extensive modifications.
3. Because we have tanks (and not just piped water) all around the yard, the pressure we achieve by gravity feed is maximised [1]. This means that we can mostly avoid pumping water in the garden (saving electricity).

System disadvantages

1. Digging the trenches and installing the pipe was a lot of work and the components were fairly expensive. A wet sump system would be cheaper overall (there would be fewer tanks, for example) though installing the piping would be more labour-intensive.
2. Some might perceive the 2 x 1 kL tanks in the front yard as being an eyesore. I will write more about aesthetics in another post

 Observations

Through a wide-gauge pipe, it is quite amazing how much water will flow even at very low pressure. Last summer, I would water the garden through a 25 mm hose with as little as 20 cm of water head (~ 0.2 psi), and found it very effective. It doesn't spray, but a lot of water still comes out if one holds the end of the hose near to the ground. Also, the water rate can be regulated by how high one holds the hose.

If I was building a house from scratch, setting up a similar system would be simpler because I would have all the gutters drain to one or two points.

A sizable expense has been the connectors for the blue-line. If I did this again, I would seek a solution that minimised the number of connectors and provide a significant saving.


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[1] When water is moving through a pipe, there is a pressure loss that is related to the speed of the water and the diameter of the pipe. By having a column of water (ie. a tank) right next to  where we want to use it, there is less pipe and thus less pressure loss.


This article was written by Angus Wallace and first appeared at guesstimatedapproximations.blogspot.com.au

Rainwater modeling

I have spent a fair amount of time thinking about water. My family and I live in Adelaide, where water is hard to come by. The energy intensity of Adelaide's water supply is about 0.8 - 1.8 kWh/kL [1], while Adelaide's new desalination plant is expected to use 3.5 - 5.5 kWh/kL [2]. Since the average household uses about 191 kL per year, the energy associated with this is between 152 - 1000 kWh per year -- a significant amount of energy.

Thus, we want to use less of this expensive resource, and more of the free water that falls on our roof and currently goes to waste. For this reason, we have installed 35 kL of rainwater tanks, and they are currently collecting from the back part of the house, the pergola and the garage. As part of my plans for developing this system, I wanted to understand what sort of performance we can expect from this system when it is completed. In other words, do we have enough storage so that we will not run out of water?

How much storage is required?

I went to the Australian Bureau of Meteorology and downloaded the all the monthly rainfall data for Adelaide [3]. Then I built a simple model that estimates our monthly average consumption. The model pretends that we installed our tanks when rainfall records began (in 1884). I then ran the model through all the data to see how our system would have performed historically. Thus we have 129 years' real data to test things.

Assumptions:

1. We collect water from every roof on our land (not currently the case, but a near- to medium-term goal)
2. We collect 85% of the water that falls on these surfaces (the rest splashes, evaporates, etc)
3. There are many assumptions about how much we use, but it seems to be approximately similar to the bills we get from our utility (although, our usage in summer may be higher than this model suggests).

Results

With our system as is (when the above assumptions are met), we would have run out of water in 100 out of 129 years.
If we capture grey water from the kitchen sink and washing machine, and use that instead of potable water for watering the garden, then we would have run out of water in 41 our of 129 years.
If in addition to the grey water, we move to a dry toilet (eg. composting) then we would have run out of water in three years.
If we increase our water storage to 45 kL, but retain the flushing toilet, we would have run out of water in 17 out of 129 years. All my modelling was performed in a simple spreadsheet that can be downloaded here [4] (the model was created in a spreadsheet in LibreOffice [5] -- a free office program that you may install for no cost if you want) -- you can play with the numbers yourself. Please let me know in comments or by email if you find any problems.

Modeled rainwater captured, in storage and consumption on a month-by-month  basis for an average year (rainfall averaged monthly since records began in 1884)

Conclusions

If the goal is not to run out of water, it is much more effective to reduce consumption than to increase storage. Also, capturing water from a larger roof area is also much more effective than increasing storage. Grey water is very powerful here, as we will be able to use water twice: once in the home (washing, etc) and then again in the garden. This is useful provided the use of grey water in the garden offsets water we would otherwise use in the garden.

Other considerations

I have also been reading about the energy cost of pumping domestic rainwater. CSIRO have published a paper on this [6], which says that having a pump that directly pressurises the pipes is a very energy expensive way to run things and results in energy consumption that is close to desalination.
I am hoping, as much as possible, to run the garden on gravity-fed water
wherever possible to mitigate this. Also, instead of having a system where a pump directly pressurises our existing water pipes in the house, I'm hoping to create a header tank up high, and then gravity feed the house [EDIT: I have decided not to do this, and have instead installed a variable speed pump. I will discuss this in a future post]. The problem is that, because we live in an urban setting, I'm limited by Council regulations how elevated such a tank can be. I will most more on this in another document.

References

[1] Climate Change and Water: International Perspectives on Mitigation...  edited by Carol Howe, Joel B. Smith, MS. Jim Henderson

[2] http://www.sawater.com.au/NR/rdonlyres/2AF55919-F858-4AB2-93E3-534E62E6DC73/0/DesalEISChapter6.pdf
[3] http://www.bom.gov.au/climate/data/
[4] https://www.dropbox.com/s/od108as4l3v4ogu/water%20calculations.ods
[5] www.libreoffice.org
[6] https://publications.csiro.au/rpr/download?pid=csiro:EP114797&dsid=DS4

This post was written by Angus Wallace and first appeared at guesstimatedapproximations.blogspot.com.au