Temp Posted March 19 Posted March 19 We had an IBC on our allotment, it had a metal frame but I doubt I could be buried. The plastic part was more flexible than a watering can.
saveasteading Posted March 19 Posted March 19 On 19/03/2025 at 09:39, mads said: the sustainability aspect of it and reducing the need for potable water Expand OK. So I specified a rwh for our own office development. Try it on yourself principle before recommending to a client. I forecast a 10 to 13 year return on capital. There were about 30 occupants, us and tenants which is rather different to a house. It paid itself in 4 years, because I hadn't thought about the sewage saving ( sewage quantity is based on water supplied). BUT I haven't included electric supply to the pump, or a replacement pump or future maintenance. Also, the duplicated pipework cost was a guess. Sustainability? How much carbon in manufacture, construction and operation? Hence my logic that you don't do it for a house not connected to the sewer.
Simon R Posted March 20 Posted March 20 On 18/03/2025 at 23:11, mads said: I'm interested what the Kingspan control system was meant to do? And if the new pump covers it all? Expand The Kingspan system has a display showing tank level and options to customise auto fill from mains water. As I mentioned the pump had failed before first use and Kingspan wanted silly money just to send someone out. Our system now is very simple. A Divertron pump which switches on when it senses a pressure change in the system ie switching on a tap. No header tank. I also bought a cheap radio tank sensor which displays tank depth. In practice it’s pretty irrelevant and the tank has never run dry. 3
saveasteading Posted March 20 Posted March 20 On 20/03/2025 at 12:56, Simon R said: the tank has never run dry. Expand That is important with long dry summers becoming more the norm. Excuse me if you've said already, but what capacity? was changing the pump very technical? ie is there justification for a specialist?
mads Posted March 21 Posted March 21 (edited) I decided to create my own calculator on how much I could save on water by RWH. Here is the calc (I included a waste water section though not applicable for me). Happy to upload the file for others to use for themselves, if helpful. I have only done it from a water consumption and waste water perspective. I have not factored in electricity costs (as I personally feel this is negligible and most of us will have PV) but have included replacement pump costs. Edited March 21 by mads 1
mads Posted March 21 Posted March 21 On 20/03/2025 at 16:38, saveasteading said: That is important with long dry summers becoming more the norm. Excuse me if you've said already, but what capacity? was changing the pump very technical? ie is there justification for a specialist? Expand Kingspan Klagster 4,600ltr system was mentioned. Re: long dry summers, I think this is where making sure you have a high volume tank is important so can store more during the shoulder months when we do have rain.
saveasteading Posted March 21 Posted March 21 Nice to see your calls. From a quick skim. The garden usage looks high. A) perhaps showing a falsely high cost/ potential cost.. b) you would empty the tank in 3 weeks of no rain. Water cost sqm should be cm ? Does waste cost belong here as a cost? You could show the saving due to lower purchase volume perhaps.
mads Posted March 21 Posted March 21 (edited) On 21/03/2025 at 13:30, saveasteading said: Nice to see your calls. From a quick skim. The garden usage looks high. A) perhaps showing a falsely high cost/ potential cost.. b) you would empty the tank in 3 weeks of no rain. Water cost sqm should be cm ? Does waste cost belong here as a cost? You could show the saving due to lower purchase volume perhaps. Expand Garden is 1 acre which will be 0.4 acre lawn, 6-8 sqm vegetable patch, medium to large greenhouse and 6m diameter pond to keep topped up, plus plants and hedging so expect fairly high use - in-laws are avid gardeners too. When I sent my request to suppliers, they came back saying I need a 5,000L tank but to be on safe side for droughts then consider a 7,500L one. I was going to get a 10,000L as I also have outbuilding roofs which I haven't factored into the water capture calc. Water cost is actually m3 - had the wrong units described and have corrected in my file. Doesn't change the calcs. Waste cost doesn't apply to me so I would zero it out. I included it in case I share this with anyone and they may need to use it due to connection to mains sewerage. For me, the ROI is around 30-40 years so one to think about in terms of capital cost outlay. Was useful to do the exercise and hope it helps others. I had to do a few iterations to get to a point where the ROI time frame balanced out. The replacement pump cost drove it up and I would look to see if 3 years is too frequent. Edited March 21 by mads 1
saveasteading Posted March 21 Posted March 21 In my office example above the calculations said use 5m3. I went for 10 which I think was right as it never ran dry. Negligible garden use. I think the ROI on the extra 5m3 would have been very short as it was only the extra tank cost...about £1k? Well done on the exercise.
mads Posted March 21 Posted March 21 On 21/03/2025 at 13:54, saveasteading said: In my office example above the calculations said use 5m3. I went for 10 which I think was right as it never ran dry. Negligible garden use. I think the ROI on the extra 5m3 would have been very short as it was only the extra tank cost...about £1k? Well done on the exercise. Expand Thanks. Though I have to say that my exercise presumes the costs stay the same for the entirety. We know that the cost of water supply is going up, with numbers of around 36% over the next 5 years. If I assumed a 3% YOY increase to the fresh water price, that goes up to 360 pence per m3 in 10 years. At that cost, it could shave off around 8-9 years from a ROI timeline. I need to do some financial modelling to see what this might look like over a 10-15 year horizon as I suspect it will be different to the static view I have started with.
SteamyTea Posted March 21 Posted March 21 On 21/03/2025 at 16:31, mads said: We know that the cost of water supply is going up, Expand Base the price on South West Water. Have I ever mentioned that we have the most expensive water and waste in the country, which probably makes it one of the most expensive in the world.
mads Posted March 21 Posted March 21 On 21/03/2025 at 17:41, SteamyTea said: Base the price on South West Water. Have I ever mentioned that we have the most expensive water and waste in the country, which probably makes it one of the most expensive in the world. Expand £348 for the year vs £304 for ST Water on a like-for-like
mads Posted March 21 Posted March 21 So some modelling shows... Over 10 years, based on a 5% YOY price increase (I think this is too low imo), the fresh water supply cost for my scenario would be: 2025/26: £304.56 per annum 2034/35: £472.47 per annum The total over the 10 years would be £3,830.72 vs £3,045.60 if the costs were to remain static. Looking at just today with the current costs, the ROI timeframe is 26.6 years Looking over a 10 year horizon with the above increases, the ROI timeframe reduces to 21.1 years Over a 20 year horizon with still a 5% YOY increase, the ROI timeframe reduces to 17.3 years
AartWessels Posted March 21 Posted March 21 I moved here from Belgium, where rain water harvesting is mandatory. We had a 5000L tank installed. Water costs around £2.20/m3 there. We used rain water for laundry, toilets and the garden. There is however absolutely no way to get an ROI, or at least not in Belgium. A major part of summer, the tank will run dry. In the wet periods, it will be full, and therefore the rain water will overflow to a drain. So the theoretical volume of rainfall can not be used, as it cannot be harvested in practice, and part of the year you will have to fill the tank from mains water to keep toilets and laundry running. Anyway, that's just my practical experience. 1
mads Posted March 21 Posted March 21 On 21/03/2025 at 18:18, AartWessels said: I moved here from Belgium, where rain water harvesting is mandatory. We had a 5000L tank installed. Water costs around £2.20/m3 there. We used rain water for laundry, toilets and the garden. There is however absolutely no way to get an ROI, or at least not in Belgium. A major part of summer, the tank will run dry. In the wet periods, it will be full, and therefore the rain water will overflow to a drain. So the theoretical volume of rainfall can not be used, as it cannot be harvested in practice, and part of the year you will have to fill the tank from mains water to keep toilets and laundry running. Anyway, that's just my practical experience. Expand Thanks for sharing. I'm interested as to why they then mandate it? And could it be different if the tank size was doubled?
SteamyTea Posted March 21 Posted March 21 On 21/03/2025 at 18:28, mads said: I'm interested as to why they then mandate it? Expand Probably as a general water management policy, similar to our SUDS. That raises an interesting point, if SUDS has to be employed, can a rainwater harvesting system replace it.
AartWessels Posted March 21 Posted March 21 On 21/03/2025 at 18:28, mads said: Thanks for sharing. I'm interested as to why they then mandate it? And could it be different if the tank size was doubled? Expand It's mandated to prevent water problems. Prevent a bit of flooding, etc. And then 'sustainability'. I don't think it's hitting either of these targets. Doubling the tank size depends on the size of your roof. Still, watering the garden in summer will suck it dry in 2 weeks.
AartWessels Posted March 21 Posted March 21 On 21/03/2025 at 18:46, SteamyTea said: Probably as a general water management policy, similar to our SUDS. That raises an interesting point, if SUDS has to be employed, can a rainwater harvesting system replace it. Expand Maybe. I'm not against storing rainwater, I just think using it in a house is not a case with an ROI. In our new build we'll store it in a wildlife pond.
saveasteading Posted March 21 Posted March 21 On 21/03/2025 at 16:31, mads said: presumes the costs stay the same for the entirety. Expand That's pretty standard. You are laying out funds that could otherwise earn interest. On 21/03/2025 at 21:12, AartWessels said: Doubling the tank size depends on the size of your roof. Expand It also depends on catching all the rain in any storm. So for a dual pitched roof there may be more drains and deeper runs. On 21/03/2025 at 18:46, SteamyTea said: if SUDS has to be employed, can a rainwater harvesting system replace it. Expand Yes, or part of the proposal at least. But anything differing from the accepted hierarchy can be difficult for a planner to accept, and you get into the need for an expert proposal. I showed planners why a harvester was better than a green roof, for example, which surprised them. 1
AartWessels Posted March 22 Posted March 22 On 21/03/2025 at 23:25, saveasteading said: It also depends on catching all the rain in any storm. So for a dual pitched roof there may be more drains and deeper runs. Expand Although I agree that is factually true, I don't think in real.life it matters that much. With that, I mean, there are so many factors in the actual environmental conditions,that you can't accommodate for all of them, not even when designing. KISS. An oversized track will hardly ever fill completely, so the tank must fit to the roof surface. Only water from the roof areas should go in. Keep your gutters clean. That has a very big impact. Clean the inflow filter regularly. Again. A big impact. In a big storm, you won't catch it all. Many reasons why not, but mostly because the time of year these usually come (the wet time), when your tanks are filled already anyway. Now, if you don't intend to use it for the house, but just for the garden, allotments, greenhouse, etc., the story changes. Using a catchment basin, IBC containers, etc. change the ROI dramatically I'd say. 1
saveasteading Posted March 22 Posted March 22 On 22/03/2025 at 07:41, AartWessels said: change the ROI dramatically I'd say. Expand The cheapest rwh I ever installed was a series of IBCs. 4m3 for £400 plus some plumbing. It was only for buckets of water for slunging vehicles OR could be set to dribble to slow down flow to drains and ground. Not pretty but the client loved the value. 1
AartWessels Posted March 22 Posted March 22 On 22/03/2025 at 08:31, saveasteading said: The cheapest rwh I ever installed was a series of IBCs. 4m3 for £400 plus some plumbing. It was only for buckets of water for slunging vehicles OR could be set to dribble to slow down flow to drains and ground. Not pretty but the client loved the value. Expand That's it. Works wonders in a rural environment, and an ROI of around 10 years if you included a pump, or less than 7 years if you don't. And maybe even less if it is in a location without any existing infrastructure.
Simon R Posted March 22 Posted March 22 On 20/03/2025 at 16:38, saveasteading said: but what capacity? Expand Our tank was is 4600ltrs. Just the two of us and a small garden. Lots of washing though as we’re both sporty.
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