'Free' Water reality check

MFW_ASAP

Cardew wrote: »

With United Utilities the charge for Surface Water Drainage(SWD) is £75pa(2014/15).

The charge is actually £79pa which also covers highway drainage that everyone who uses UU sewers has to pay for, which is £38. The reduction for having our domestic surface water diverted into a stream is therefore £41 per year (£79 - £38).

Cardew wrote: »

To reduce your bill by 50% even allowing for SWD deduction, I calculate you will need to use approx. 95 cubic metres of rainwater pa.

Sorry, I'm not sure what your point is here?

Cardew wrote: »

That is also assuming that you don't intend paying the sewerage charge of £1.264/cubic metre for rainwater you are diverting into the sewer via your house;)

United Utilities dont meter the rainwater used or the amount of fluid entering the sewage system and so their charge for sewage is calculated on the amount of water they have supplied. They simply state that you cannot claim the £41 per year surface water rebate if you have a rainwater recycling system, which is logical and fair enough.

I guess the question is whether I apply for the £41 rebate when I divert my rainwater to the stream and neglect to mention that I'll be installing a tank at some point in the future. I'm not sure £41 is worth being devious, to be honest.

Cardew wrote: »

I am a little puzzled why you need to store rainwater, when it would surely be easy to divert/pump water from your stream to a tank?

What Martyn said, especially the gravity feed of the rainwater rather then having to buy and run a pump for the streamwater, plus I would have to dam the stream in summer as the stream goes down to a trickle and undam it in winter when it rises to a torrent. As I said, I want a 'fit and forget' system.


　

Cardew

Quote:
Originally Posted by Cardew
To reduce your bill by 50% even allowing for SWD deduction, I calculate you will need to use approx. 95 cubic metres of rainwater pa.

Sorry, I'm not sure what your point is here?

Just wondering if a 5,000litre tank would be replenished - particularly in summer - when you will be using approx. 2,000litres a week.


If you do a search on MSE iirc there were a couple of threads with useful information on both rainwater and grey water recycling from people who had installed systems - might have been in the Energy(water) section.

MFW_ASAP

Cardew wrote: »

Just wondering if a 5,000litre tank would be replenished - particularly in summer - when you will be using approx. 2,000litres a week.


If you do a search on MSE iirc there were a couple of threads with useful information on both rainwater and grey water recycling from people who had installed systems - might have been in the Energy(water) section.

I used an online form to calculate the size of the tank (from the rainwater harvesting site I linked). Maybe I need to look again?

Martyn1981

MFW_ASAP wrote: »

I used an online form to calculate the size of the tank (from the rainwater harvesting site I linked). Maybe I need to look again?

Eric (Mears) is your guy for rainwater harvesting on this board. He's also got 5m3, but I don't think he uses as much as you.

Thinking about this, I guess it's the same cost of storage v's worst case that the off-gridders I chat with use for sizing battery banks. Rather than work on the worst, they go for a reasonable size, then accept that they'll use a genny for longer 'bad' patches.

Since you already have a replacement supply on tap (ha ha) for any shortfall periods, try to work out just how many days it's sensible to provide for, rather than spend a fortune to meet the rarer extremes.

2+ weeks sounds like a sensible start. Does a larger tank add silly costs to the project? I assume it's more an issue of the additional groundworks and inconvenience that will determine the sensible size of your system.

Don't forget to keep a photo log of the project for others to learn from, and for nosey folk like me just to see how it all works.

Mart.

EricMears

Martyn1981 wrote: »

Eric (Mears) is your guy for rainwater harvesting on this board. He's also got 5m3, but I don't think he uses as much as you.

We have 4 x 1 cu m tanks in our basement and 2 x 250l header tanks in the attic. (We've also got another 5 x 1 cu m tanks in the garden but they're only used for watering garden)

There are only two of us in the house most of the time and I tend to need to pump 100 litres of water from basement to attic every day. At this time of year I do that just before 8am using E7 power; for most of year I can do it on free power during day.

When first set up we only had 2 x 1 cu m tanks in the basement and there were three of us in house (but house was unoccupied during daytime). We'd run out of rainwater for a couple of weeks in the summer most years. Since adding another couple of tanks (and sending son off to uni) our basement stock very seldom drops below 2 cu m even though house is now occupied during day.

Our water bills tend to be around £60 per half year. That's purely standing charges + metered water as we have no public sewers within a mile or so, so excess rainwater goes to a soakaway and sewage to our own septic tank.

MFW_ASAP

UPDATE:

Now that the weather is nice and I've been enticed outside the house, I started quietly digging away with my trusty spade and I'm slowly disconnecting the rainwater downpipes from the sewer line.

We have three downpipes on the main house (the roof covers 160m²) and two downpipes on an outbuilding (the roof covers 60m²). So far I have severed one of the downpipes by digging out the connection between the drainpot and the sewer line and capping the outlet from the main sewer pipe with a plastic bung covered with cement. I removed the connecting pipe and drain and replaced it with a rainwater gully to trap any leaves that might come down the pipe:



I've temporarily connected the outlet from the gully to the french drain while I now dig a channel to the second downpipe on the side of the house. Once I rech there, I will cap the sewer pipe and fit another rainwater gully, connecting the two together and then makemy way around to the third drainpipe. The costs of this are pretty minimal as I'm using plastic piping which is really inexpensive.

There have been a couple of benefits already - the existing downpipes never really met the existing drains (blame the poor workmanship on the person who renovated the house) and so some rainwater missed the drain and soaked into the foundations of the house. The drainpipes now go directly into the gully, which is sunk under a couple of inches of gravel, so all you see is the drainpipe dissappearing into the ground - very neat.

The second benefit was that we had a sewer blockage recently and the blackwater backed up. It was a simple fix for United Utilities to fix (tree roots in the drain) and I had forgotten all about it until I started to dig out the drain. There was a 'sewer' smell and 'soil' around the rainwater drain, caused by the sewer backing up. Disconnecting the rainwater pipes from the sewer pipes means that we will not have this gross issue occurring again, should we have another sewage blockage!

I'm hoping to get all of the downpipes connected to each other this summer, with them temporarily going to a junction installed at the point where I intend fitting the tank. I will also connect a pipe from this junction to the existing outlet to the stream. The plumbing will kinda look like this:



Once the external work has been carried out, I'll order the header tank and 'rain director' box and connect it to the mains supply and the output to the toilets and washing machines.

All that remains is then to install the tank (5000l Graf Platin below) and connect it to the header tank.



The biggest expense will obviously be the raindirector, header tank and main tank, with the remedial plumbing just the cost of a few plastic gullys and pipes and my own free labour.

zeupater

Hi

Any update yet ?? ... is it completed ? .... did you go for a 5tonne system or decide on a larger tank in order to provide a healthier buffer considering the 2tonne/week usage ?

Z

MFW_ASAP

Thanks for the interest.

I'm still digging out the channels and laying pipework I'm afraid, so no update as yet.

I did look at larger tanks but read that a lot of rainwater harvesting companies recommend tanks that are oversized in order to increase their profit (larger tank = more money), but that it increased waterborne disease risks due to water stagnation.

According to many sites I researched, the safe way to determine the size of the storage tank was to calculate the amount of rainwater you receive (using rainwater tables, the size of roof collecting the rain and the type of roofing material) against the water useage in the home (using info on number of people in the house, number of toilets, washing machines, size of garden) and using the smaller figure to calculate your tank size.

It seemed a logical suggestion as too large a tank will never be filled if you have a small roof and even if it is filled, it'll stagnate if you only use a few litres a day to flush a toilet.

I used an online form that asked the above questions (and included a safe amount of extra water to cover a drought) and it suggested a 5000l tank, so that's what I'll go with. I dare say that during extreme periods of heavy rain I'll be kicking myself for all that 'lost' water (though I wouldnt be able to use all this water anyway!) or during periods of drought I'll be lamenting using tap water for flushing toilets, but you can't spec a system (and have the additional costs) for cases that may only occur very rarely, perhaps only once or twice in the system's lifetime.

MFW_ASAP

Here is a link to one of the sites I found that discusses tank sizes and waned against oversizing a tank (and they're a tank manufacturer, so it's refreshing to see they're not trying to sell larger tanks at the expense of their client's health!)

http://oasis-rainharvesting.co.uk/sizing_the_tank

How to size your Rainwater Harvester

The tank size for a rainwater harvester is not entirely your choice. If the tank is too large then you run the risk of bacteria breeding over time to dangerous levels. For this reason, a tank size calculator, based on average annual rainfall and water usage, has been developed by the British Standards Institute in an effort to stop companies trying to make more money by encouraging the sale of bigger tanks.



The BS 8515 2009 states that the capacity of the rain water harvesting storage tank must be the LEAST of either:

• 5% of the Annual Rainwater Yield (ARY) or
• 5% of the Annual Rainwater Demand (ARD)

To calculate the Annual Rainwater Yield (ARY) use the following calculation using the rainfall map below

Rainfall (mm) x Building Footprint Area (m2) x 0.9 0r 0.8 (Tile Roof or Slate/Stone Roof) = ARY
ARY x 0.05 = 5% ARY

To calculate the Annual Rainwater Demand (ARD) use the following calculation:
No. of Residents x 16,000 = (1) Area of Garden (m2) to be watered (if any) x 60 = (2)
(1) +(2) = (3)
(3) x 0.05 = ARD

You are not allowed to install a rain harvesting tank that is larger than the smaller of these two figures as the water will become stagnant and a breeding ground for bacteria, including Legionnaires Disease.

MFW_ASAP

Using the calculation above, the Annual Rainwater Yield (ARY)for our house comes to 6400 litres and the Annual Rainfall Demand (ARD) is 4800L.

Taking the lower of the two, I should go with a 4800 litre tank, bu I'm assuming an extra 200l is neither here nor there, so I'll go with 5000L.

I'm guessing from the calculation that the British Standards Institute has assumed an annual water useage of 16,000 litres (non-potable water so no bathing or drinking, just flushing a toilet and washing clothes). That's 43 litres a day. According to the 'tinternet, the average toilet flush uses 4 litres of water, so I can go to the loo 10.96 times per day!

According to the same site, an average washing machine uses 50 litres per wash. At 4 washes per week multiplied by two washing machines, that's 8 washes totalling 400 litres. Divide that by 6 people, it comes to 66 litres per week or 9.52 litres per day.

Therefore with my 43 litres per day reduced by 9.52 (call it 10) litres for the washing machine, that leaves 33 litres for flushing the toilet - or 8.25 individual flushes.

If these figures are correct then I should be OK except during periods where a dodgy curry is consumed! However, this doesn't take into consideration that 4 of the six of us are out all day at school or work, and will therefore be poo or wee flushing with non MSE_ASAP stored water.

5000 Litres should be OK for us I think.