My DIY rainwater harvesting project

I've been putting together a rainwater system to feed the toilets in our house and I thought I would share the how and the why, partly to pass on what I did and partly to get feedback and see if maybe there are better ways of accomplishing what I did.


Background

I'll keep this bit short as most folk will probably just want to know how it is put together. The original idea for this came from occasional but frustrating water outages due to our very low water pressure. We're at a height in Ashbourne and the pressure is just on the threshold of acceptable normally, but if there is a long
period of low rainfall then our pressure drops and the water doesn't even make it up to the tank in the attic. This has happened at least twice a year.
As well as that, when the water tax was confirmed as coming down the line, I thought this was a no-brainer and decided to pull the trigger on the project.
We have three toilets in all, and this project would convert two of those to use rainwater, the upstairs toilets. The downstairs toilet is too difficult to pumb in as
the supply pipe is hidden in the wall somewhere and it also supplies the hand basin. That would have been a major job involving pulling plasterboard off the wall and
that's somewhere I did not want to go. Plumbing in the upstairs toilets would (only!) consist of bringing a new pipe down from the attic and splitting that to supply
two adjacent rooms.


The Build

I have to start off by saying that I was not sure at the beginning if this was really going to work, so I didn't spend big on anything. Also, it was going to be a staged build as I wanted to see if one part worked properly before building the next.

The basic parts are:

- drainpipe diverter
- filters
- storage barrel(s)
- 2nd attic tank
- submersible pump
- pump controller
- mains backup mechanism
- associated plumbing parts


The collection starts with a square drainpipe diverter that links to a length of pond-pipe. Due to space restrictions, the only place the tanks could go was in the corner farthest from the drainpipe. That meant the pond-pipe was going to have to run the whole length of the back wall. Not pretty, but it was the only way.


[URL="[URL=http://pix.ie/yerman/3736305][IMG]http://photos3.pix.ie/9B/E1/9BE1AFC6AE1D43B89B975B60242D9606-0000314530-0003736305-00640L-9304794C45C94B96BA920435A8C958FC.jpg [/IMG][/URL]"][/url]


Within the diverter, I put the first stage of filtration, a wire mesh funnel. The idea is that lumps of moss etc would hit that and slide off down the drainpipe; water would seep through the mesh and enter the connected pipe. The next stage is filter no.2, one that is normally fitted to a pump, but I have it on the divert downpipe. This one is easily accessible and can be cleaned out when needed, all it needs is a scrub. I also have the filter wrapped in a black pastic bag to stop algae growth as that makes cleaning harder and needing done more regularly.


[URL="[URL=http://pix.ie/yerman/3757433][IMG]http://photos4.pix.ie/48/01/480116B0086D4F8E9F64A3489AB803A5-0000314530-0003757433-00695L-6084074AB05F49C8AE9E77DA9ED1D891.jpg[/IMG][/URL]"][/url]


Finally, the third filter is an idea I got from a Youtube video. It's a milk filter sock, the type used by dairy farmers. I have it stuck on the end of the downpipe. These fabric tubes are cheap and bought by the 100. I got these in an agri-suppliers for less than a tenner. I don't know the micron-level of filtration, but they catch the smallest bits of dirt that pass through the 2nd filter and the sock needs changed about once a month.



[URL="[URL=http://pix.ie/yerman/3736312][IMG]http://photos3.pix.ie/97/76/9776B29BD3B548299159BC6D2C63C231-0000314530-0003736312-00500L-C01D0B45B5D74D62B259DBF250E46B70.jpg [/IMG][/URL]"][/url]



The collectors are two 210-litre water butts I got in Aldi, but I see their design in garden centres all over the place. I have them connected at the bottom and also anchored to the wall. They are some weight when full and I don't want kids to get hurt it they somehow were to topple over. 420 litres sounds a lot, but for this purpose, it actually isn't. More on that later.


[URL="[URL=http://pix.ie/yerman/3736309][IMG]http://photos3.pix.ie/85/40/8540A8C631E940ACB4510048B90FC3A2-0000314530-0003736309-00500L-307F9BCF3F784E04B50A0D2301723972.jpg [/IMG][/URL]"][/url]


So how to get all this clear water up to the tank that awaits it in the attic? I have a submersible pump (also purchased in Lidl) suspended in tank 2, connected to a looooong piece of qualpex pipe that goes directly to the tank, without any joints inbetween. This is a 240v pump, and the power cable also goes all the way up there to a socket.


[URL="[URL=http://pix.ie/yerman/3736301][IMG]http://photos3.pix.ie/D6/10/D610AB63C28B4528B4BE1472A0A9F6E4-0000314530-0003736301-00640L-F2D41FB5BA204E95B96A27BA9759D671.jpg [/IMG][/URL]"][/url]


The controller for the pump is worth a separate post on its own, but I'll summarise it here. Having a technical background, I wanted to build a controller myself, so I started with a Raspberry Pi board. On this board are connector pins that can link to sensors to detect water levels and relays that can turn on power. I bought float sensors and put them in the collector barrel and the attic tank and wired them to the Pi. With those in place, I could then detect if there was enough water in the barrels, and also when there was not enough water in the attic tank. Also attached to the board's pins was another board of relays that would connect the Pi's low voltage control to the pump's high voltage supply, enabling me to turn the pump on and off at will. Using a scripting language (Python), I then wrote the logic that would control when the pump had to turn on and, more importantly, when it should turn off. Because it's my own design and I know the programming language, there is a lot of flexibility in what I can do with the controller. At the moment I have it sending me emails of how each pump session went, and it also tracks how much water it has pumped.


[URL="[URL=http://pix.ie/yerman/3736307][IMG]http://photos3.pix.ie/1D/9E/1D9EED64FB3149AC9F3945730980EAF1-0000314530-0003736307-00640L-0FEFC498F4DC41269639A3F95E28B547.jpg [/IMG][/URL]"][/url]


And what if it doesn't rain for ages, like Summer 2014? What is going to supply the toilets then? That's where the mains backup comes in. There was no way we could rely solely on rainwater so a decent mains backup would make up the shortfall. Initially I wanted to have this as a mechanical backup, akin to a ballcock in a toilet cistern (techically called a part-fill valve). I wanted to make sure that in a power outage a non-electrical backup would still be functional. But the part to make that work came to almost the same as had been spent on the lot so far and I just couldn't justify it. (part-fill valve example) So I had to rethink that bit and reluctantly went with having the mains backup also controlled by the pump controller Raspberry Pi. I fitted an electrically-controlled water valve to a pipe Teed off the mains supply to the original attic tank and added the logic to the controller's program so it would open the valve if there was not enough in the barrels and the water level was low in the attic tank.


[URL="[URL=http://pix.ie/yerman/3736310][IMG]http://photos3.pix.ie/54/2C/542C02ED42E04BB1A509F62F7CD0E0ED-0000314530-0003736310-00800L-8B0F7BBC944B490B9A73F37288601404.jpg [/IMG][/URL]"][/url]



Results

---

So after all this, a project which on and off took most of last year, it has worked mostly as I planned, apart from a couple of occasions. I have yet to analyse the stats in detail but I would estimate perhaps about a third to a half of our toilet flushing needs have been met by rainwater. That includes having a few extended periods with no rainfall where we live too. Mains backup kicked in then and kept the attic tank at a minimum level. There have been two occasions when the tank ran dry though, causing an airlock in the cistern supply pipes. Once was early on when I had programmed just two tank-check times a day, when the controller would check the float sensor levels and work out if a rainwater or mains fill was required or not. I quicky learned that a morning and an evening check was just not enough for normal use, so I changed that to a check every two hours in daylight hours. Another time, we had visitors staying over and the tank was also on mains backup at that time. With higher demand from more people, it quickly went below the minimum level well before the next check. I had to do a forced manual mains-backup fill using another program similar to the main check script, running the mains backup for longer until it reached the float sensor at the top of the tank that would signal the cut-off.


Improvements to be made

- A bigger storage volume is required. I plan on moving up to an IBC tank holding 1000 litres next.

- A more intelligent control algorithm. There are a few things to change here, now that the system has bedded in. At the moment it is a bit on the paranoid side as I do not want to flood the house if something goes wrong. But it needs to have a better mains backup fill method than it has at the moment.

- Currently only the drainpipe at the rear has a diverter, so I'm missing the water that falls on the front part of the roof. That will be a bit of a challenge as the diverter will have to be even higher than the rear to keep the water moving by gravity.

- there's probably more and I'd appreciate your feedback. I know others have put their own systems together, so I'd love to swap tips too.



Cheers,
B.