Chapter 1. Introduction

On sustainability projects apparently rainwater is often overlooked. I almost overlooked it myself, something which would have been unforgivable on an aquaponics project. Just in time however I figured out that a well planned rainwater usage could bring great benefits. In the Netherlands the typical drinking water usage for a family with 4 persons is about 169 cubic meter or 19.60 euro/month. For my own family I wouldn’t be very surprised if it would be higher than that and particularly with the planned aquaponics installation I think it’s safe to assume a 50% extra, so about 21.000 liter/month, or 29.40 euro/month. Not all the water that we use can be replaced by rainwater, however

  • fishwater
  • laundry machine
  • toilet
  • and possibly bathwater

can easily be replaced by rainwater. A cautious assessment is that this could be 50% of the average usage or about 10.500 liter/month.

Chapter 2. Sewer

I actually thought of this subject because the installation for the majority of the equipment for our greenhouse project will be concentrated in the garage. I was wondering if I couldn’t change part of the garage into independent office space. I had checked into this possibility before as the expenses for creating and using such independent office space are fiscally deductable. However, my earlier investigations revealed that this would require having its own independent sanitation and entrance. At the time digging a waterline from the house to the garage didn’t seem feasible.  As we will soon be digging for the heat/cold storage however, it seemed like a good idea to put a waterline in the ground. However, then I’d still not have a sewage connection for that toilet and a rather long horizontal sewage pipe back from the garage to the house didn’t seem like a very intelligible solution. However, the garage has its own rainwater drain to the sewage, so I started investigating whether it would be allowed to let toilet waste go through that. My search revealed that it is in fact NOT the sewage water that causes problems but the rainwater! The government subsidizes in several communities to ‘disconnect’ people’s rainwater from the sewage. This is because the rainwater can quickly exceed the sewage’s capacity and it also dilutes the sewage, making it harder to cleanse it. Only then it began to dawn on me that recycling rainwater may be a hotter item than dealing with the garage’s (potential) sewage.

Chapter 3. Digging

As I will soon be digging in my back yard, I quickly started researching possibilities with which I could store rainwater. Preferably I’d do this underground because without any light, no algae will grow in it. Aside from that it looks a lot better. Underground storage tanks for rainwater are pretty expensive. A 3000L watertank as pictured below easily costs about 1300 euro.watertank3000L would probably not even be enough for our usage of approx. 350 L/day (21000/30/2) since it would have to rain enough every 3 days to fill a 3000L tank. A much nicer solution is to couple so called ‘IBC tanks’. IBC tanks are (often) 1000L containers with a metal frame around it that take care of the strength. However, they’re not built to be used underground; the walls could then get inwards pressure from the dirt and they’re not designed for that.  Some reports however have shown that with some board to reinforce the sides it can be done quite well. Additionally, IBC tanks are priced very nicely and can sometimes be found for as little as 25 euro each. ibc-container_7FRMQ_large

For the fishtanks we had also considered these tanks already. Here the argument was that they’re easily put next to each other and coupled so it would make a nice modular system where different breeds/sizes of fish can be held after the top has been removed. The plan was to dig a trench in which the IBC tanks could be standing, with the top slightly above ground for easy access. This appears to be a reasonably good solution for the rainwater tanks, however it would mean we would get light in the tanks and algae growth. For now however we’ll be putting them underground with boards to reinforce the sides. This will make maintenance a lot more difficult but there won’t be much traffic where we’ll be digging them in so fluctuating pressures should not occur too often.

Chapter 4. Prefilter

Online I found a nice solution to remove small leaves and branches (and in fact much smaller pollutants as well.) This is the T33 dBCOM as shown below.


This filter will be placed in the rainpipe and has self-cleaning properties. Half of our garage roof is connected to the neighbor’s sewage installation; conceivably I can also let this flow into our tanks, requiring 2 of these filters. UPDATE Jan 17th 2014: Cool, I just got the rainwater filters delivered at home. This weekend I’ll probably not get to digging yet but at least I’ll be able to install the first rainwater tank as a try-out. DSC00230

Chapter 5. Expenses

As we would like to store at least a week’s worth of water in our tanks, we decided we would install 4 of these IBC tanks. The T33 costs 33 euro, the IBC’s total about 100-200 euro, so the total expenses come to approx. 260 euro, including some PVC maybe 350 euro. If the usage numbers are a close approximation of the real usage, we would be saving about 15 euro/month, making this investment earn itself back in 2 years. The digging required for this is already calculated into the heat/cold storage expenses. UPDATE 14 Januari 2014:  The City Council of Almere informed me that disconnecting the rainwater from the sewer is not subsidized. I have decided to start a  ‘burger activiteit‘.  Through collecting 50 signatures and submitting a form, the City Council can be asked to put a subject on their calendar. Therefore, through this site I will ask Almere residents to submit their name, address and email address in order to collect signatures and inform them (optionally) electronically about the progress. UPDATE 16 Januari 2014: Well, our IBC containers have been delivered. They sure look a lot more intimidating than I had anticipated!! DSC00226

UPDATE 19 Januari: I wanted to dig the first rainwater hole manually. I guess it’s a matter of respect. It wasn’t easy as you can probably guess from the size and depth of this hole. Yesterday I didn’t make it deep enough and put the contained in there for sizing. Well, the hole was too small and the container got hopelessly stuck in it. Today I fixed that. Still not fully at the right depth but I’m considering taking the bottom part off the IBC containers.

UPDATE Januari 26th: Last  weekend I’ve been very busy with some rather trivial work. I’ve decided that the IBC containers shouldn’t go underground. The metal would rust through too quickly and cause a lot of polution. The wood would rot too quickly and cause the containers to slide deeper into the ground.

So I’ve been busy stripping the IBC containers. First take out the two metal bars from the top and the plastic containers can be slid out very easily. Then we’re still left with a fairly heavy cage with an even heavier pallet attached to it at the bottom. Together with Marissa we unscrewed the cages from the pallets. After that I cut the cages at the corners so now I have 12×4 = 36 sides left. Possibly we can reuse these metal sides, they seem like good racks to let plants climb up against.

After that I removed the bottom layer off the pallets. Most of the bottom layers are in such a bad shape already that they’re difficult to reuse. The top sides can now easily be lifted and I believe the wood can be reused for other purposes.

The now stripped IBC containers could be put underground IF they would be filled with water all the time. For the rainwater containers however this won’t (always) be the case. This is why we’ve been brainstorming about a solution to this. The solution we came up with was that Tracy, Lukas and me went out to get 56 free 60x40cm pavement stones from somebody’s backyard. I want to use these as floor and side walls for the rainwater containers. After all, why would we make a concrete wall when you can help out somebody else by lifting some ready-made concrete tiles from their yard for them. One challenge that still remains is to see whether the pavement tile walls will be stable when they’re squeezed between the (possibly empty) IBC’s on one side and the ground on the other side. Perhaps I’ll need to make some wood support on the inside of the pavement tiles still.

I also found the connectors pictured below to connect all the IBC containers together at a French company. They were quite affordable compared to some other quotes I’ve received. The S60/6 connectors are apparently not as mainstream yet that there’s mass production prices.  Multitanks however has a pretty good selection already and very decent prices. I paid less than a 100 euro for 12 T-connectors and 24 Gardena connectors. Now the containers can be coupled with flexible hoses.

t gardena

UPDATE 4 Februari: I decided to dig the rest of the hole for the rainwater containers manually after all. Mostly it was an effort to entice my kids into helping me with the digging in order to earn some extra allowance. After all it’s a family effort! Unfortunately they did understand this but did not realize that I had been digging all of sunday afternoon.

The hole is now on depth, the largest part of the walls has been covered with pavement tiles. Unfortunately last night I injured myself because a pavement tile that was standing up vertically decided otherwise and landed on my big toe. A short visit to the emergency post fortunately showed my toe wasn’t broken, but the bruise is going to keep bothering me for a while. In any case I should be able to place the containers the coming weekend and connect them all up.