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In the last years I have been very concerned about the incredible waste of water from washing machine that could be easily used for toilet use, but up to now I have not found an easy way apart from filling some containers and manually lifting them for toilet use. This is a very unsatisfying solution as the containers (around 20 litres) are heavy and the filling needs to be always supervised. Are there ways to easily connect waters from washing machine to toilet in a more efficient way? Do you know if this solution has been thought of by engineers? In my two years experimentation I have reduced the water consumption by half. I think this would be a very interesting way to have a sustainable water consumption in the house, leaving clean fresh water only for important processes (cooking, dish washing, personal hygiene...) Thanks for replying.

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Most washing machines pump water out. The pump is not intended to have a very high "head" or lift distance above floor level, but must have enough pressure to pump water above the level of a wash-tub as this is usually what is used as the water drain. Such pumps will be able to pump water "somewhat higher". Flow rate will drop with increasing height, but a tank mounted slightly above toilet tank level will be able to be filled. From there it is "easy enough" to take a pipe to the toilet water inlet. If desired you could use an independent inlet with its own valve so the mains feed is left in place with the tap turned off.

Note that washing machine water will contain soap scum and dirt from clothes, which is liable to build up in storage tank, cistern and vales and pipe and need occasional cleaning. Filtering, settling and careful positioning of the toilet feed pipe entry will minimise this issue.

A small electric pump could be used to transfer water from a lower level tank or a handpump could be used. You may wish to figure pump and pumping costs into your calculations if you want to know how "green" your solution is overall. In my country (New Zealand) the water for a toilet cistern fill costs about 3 cents and the electricity required to lift this one meter (assuming a fairly inefficient system) costs about 0.01 cents, so the reuse costs about 300 times less. Electric pumps can come from windscreen washer pumps (good lift, low rate, more easily blocked, usually 12V operation), electric washing machine pumps (fairly ideal: mains powered, OK lift, find in junk-yard) and more. Only some washing machine pumps are electrically powered - older ones tend to use mechanical drive using the main motor.

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All you need to do is position a tank (herein called catchment tank), large enough for the wash water volume, above the height of the toilet tank with a downspout into the toilet tank inlet. It will be helpful to place a tightly woven screen or loosely woven synthetic fabric over the outlet of the catchment tank. That will filter out most of the debris that would interfere with the operation of your toilet's fill valve. You will also want an overflow drain positioned so that excess wash water doesn't overflow the catchment tank.

There is no need to pressurize the catchment tank, gravity can do all the work, just keep in mind it will fill your toilet at a slower rate than the fresh water supply does. The rate of fill will be determined by the diameter of the pipe between the catchment and toilet tanks, and more importantly the difference in their height. The frequency you clean the filter will vary with your usage and filter material.

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If you really want to save water, stop using water in your toilet.

Use a composting toilet or a low flush toilet without a cistern.

100% of the water we use in our house goes into a 7000l below ground tank with a submersible pump in it. The pump has a float switch that then pumps the water out into the garden to water the vegetables.

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    +1 I like your more systemic solution. Not only catching laundry water, but all "grey" water from basins, showers, baths, dishwashers, etc. It helps if your house is designed from the start (or can be modified afterwards) to have all the outgoing plumbing to empty into a single tank, or sump, from where it can be pumped higher for reuse. A simple DIY sand+activated carbon filter may be able to reduce scum&dirt a lot, e.g. for toilet use, but apparently plants are happy with the extra nitrogen compounds in the soapy water. – fr13d May 17 '16 at 14:57
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    I also have a fat trap in-line before it gets to the below ground tank so that fat and floating solids can by removed automatically before entering the grey water tank. The laundry outlets also have an external lint trap to catch anything from the washing machine and laundry trough. – Jason Pascoe May 19 '16 at 6:37
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I have just started recycling our Laundry Grey Water on a farm in Australia through the Toilet Cisterns. I initially had an IBC 1000litre tank on 200 litre (44 imp gallon) oil drums outside a verandah with a step down from the verandah floor of about 300mm (1foot). The washing machine would only just pump in when the tank was empty and no way would fill the IBC (Intermediate Bulk Container- plastic with Aluminium frame around it). I have since bought a used 240v pump for $80 to fill the IBC. At half full there was not enough head to fill the toilet Cisterns even though is was running in by gravity. I am now moving the IBC to under our garage to get another 600mm (2 feet) head. This places the bottom of the IBC well above the Toilet Cisterns. The washing machine uses approx 48 litres per full cycle and the toilets use 7 litres per flush and 1 person full daily use amounts to approx 50 litres of flushed water. The toilet water goes down to a septic tank and French Drain at the end of which I have another IBC to hold all bathroom and laundry/toilet water for use on fruit trees. I hope these ideas are of use to someone. I am now enquiring about council and health regulations here to start a business doing this cycle.

  • Is soapy laundry water good for fruit trees? I have always wondered. – RedSonja Oct 4 '16 at 13:13

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