Browse Forums Eco Living 1 Feb 15, 2014 1:52 pm Hi All, I've greatly enjoyed reading the water tank articles on this site. But they also make me slightly worried because we have done nothing like the planning thats being done here. We have placed a great deal of trust in a well recommended plumber, who I'm not sure has done much more thinking about the project than show up and connect up the tanks. I'd be very pleased to get the advice of people here who have been through the process. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ In short, water from rooves is captured in tank 1 and periodically we pump it up to tank 2 where it is gravity fed into the house. We want to make a simple, efficient system. We're poor, but can afford to not cut corners that will cost us down the line. We used http://www.ata.org.au/tankulator/index.php to estimate the size of our tanks. Location: Geeveston, Tasmania. Rural setting, no town water. Fire code says we need 10kl of water for firefighters. Its not available to us but we provide the capacity. No trees near house (yet) Nothing is built yet. Tanks are not delivered yet(but soon). Tank beds are not made yet. Tanks: Already orders 2 X 22kl stainless steel tanks. They are 2.4m tall. Tank 1: at the same level as the house, existing drain runs behind tank that could be used for overflow, on 100mm of bluestone. Only 10kl of water available to us though. Tank 2: up the hill and 100m from house, on 100mm of bluestone. Catchment: From roof of shed to tank 1. Hopefully a dry connection. From roof of house to tank 1. I think this has to be a wet connection. Supply: Under gravity feed from tank 2 over a 50mm polypipe. About 15 m of head (I think its at least 15). So there are 2 pipes running to tank 2. One 25mm supply line fed by a pump from tank 1. One 50mm outflow under gravity to the house. House/shed: House is about 10m from tank 1, shed is right next to it. House has mixer taps. Gutterlines is 2.7m high. I'm assuming first flush diverters have to be at the house and shed. Tankvac, waterboy, gutter leafguards? I'd be very interested to have comments on the design. Firstly, is it OK? Can it be improved? Are there things I might consider? Secondly, what do I say to the plumber to make sure I get what I want? Bonus points for answers to: How do tell how much water is in tank 1? Is it easy to attach a float cutoff valve to tank 2 and set a pressure switch at the pump such that it stops pumping when tank 2 is full? (I'm hoping I can set it to start once a month and stop when tank 2 is full). cheers, tasman Re: Simple water tank design 2Feb 16, 2014 12:03 pm Hi tasman, Thanks for all of the good information and the diagram. It’s easy to tell that you have been reading the threads. RAINFALL AND YIELD You have a reliable and consistent annual rainfall of about 870 mm. You also have clean air, a great combination. http://www.bom.gov.au/climate/averages/ ... 4137.shtml 1 mm of water on 1 sq m = 1 litre. Your climate and rainfall pattern will provide an annual average yield of about 90%. Most yield losses occur during days of light scattered showers whereas days with consistent rainfall have high yield. Your 240 sq m total roof area x the average annual rainfall of 870 mm x the .9 yield will give an average annual harvest of 187,920 litres or an average of 514 litres per day. First Flush Diverters fitted with ‘drippers’ will substantially reduce yield. If possible, you should use a first flush diverter that can be manually drained so that the water can be collected for the garden etc. Manually drained first flush diverters need to have the water that enters the capture chamber first pass through a fine mesh so that leaves etc do not block the outlet. This is managed by fitting leaf diverters to the downpipes but doing so sacrifices head. Have you calculated what your average daily indoors use will be and will there be a consistent outdoors demand? This influences how to best design your system. PUMPING FROM TANK 1 TO A SECOND ELEVATED TANK The worst quality water is at the bottom in the anaerobic zone. For best results, you should let water settle for a couple of days after rainfall before pumping it. Fitting the settling tank with a floating suction pipe is a good idea. You could make one, have one made up or buy a commercial product like the WaterBoy you mentioned or the Waternymph. The alternative is to have the pump draw valve installed several hundred mm above the bottom of the tank if possible. I would not have a submersible pump as they do not draw the best quality water. You will need to pump more often than once a month. You will need a fire fighting outlet fitted at the bottom of tank 1. Have you checked if the fire service has a particular size and type requirement? You will also need a low drain valve for other needs. Have you also considered an emergency situation where you may need to transfer water back to tank 1? When transferring water to an elevated tank, most plumbers will plumb the transfer pipe up the side of the higher tank so that the water flows in through the top inlet. This is inefficient. The best method is to feed the water in through an inlet fitted 100-200 mm above the bottom of the tank. This is not only neater and easier, it is also more efficient as the total head is then to the surface of the water in the tank and not to the top of the riser above the tank. The weight of the water in the tank will not impose any additional flow resistance as it is pressure, not weight that provides hydraulic resistance. If the elevated tank is ¼ full, it might have let’s say 550 mm of water but the top of the riser could be nearly 2 metres higher. While the 550 mm of water (about 5,500 litres) will weigh 5,500 kg, the pressure exerted will only be .55 x 9.8 kPa = 5.39 kPa. With this example, the pump will initially save pumping an additional 2 metres of total head. More total head = slower flow = less efficiency. How difficult will it be to locate the second tank at the elevated site? You could perhaps have both tanks near the house and use a large pressure tank if there are issues. A 28 psi tank is just over 190 kPa. 1 metre head = 9.8 kPa. 1 psi = 6.89 kPa. DRY SYSTEM DIVERSION FROM THE SHED The 90 sq m shed roof should be able to transfer water during a 1:20 ARI through one dry pipe. You should use a 100 mm PVC DWV pipe rather than flimsy 90 mm stormwater pipe. The roof area would normally need two downpipes but shed roof drainage is still not regulated as far as I know. I am also assuming that it is not a gable roof and that the pop will be fitted midway with the gutter’s high points at both ends. What is the gutter length? If I know this, I can calculate the flow during a 1:20 ARI for the intended slope for various cross sectional size gutters. Alternatively, whoever erects the shed should know how to do this. As it is a straight length of gutter, the actual regulation tables referenced become reality BS. AS/NZS 3500.3:2003 table 3.3 shows that you need a 10,000 sq mm cross sectional gutter and a 125 mm round downpipe! There is only 300 mm between the bottom of the gutter (2.7 m) and the top of the tank (2.4 m) IF the tank sits on the ground but it won’t because it will sit on a 100 mm base. It is important to know where the tank’s meshed inlet is and whether the tanks have flat rooves. If the roof is flat, then the top meshed inlet will also be at 2.4 m. Knowing the inlet’s height is critical. The gutter’s pop fits into the downpipe and this is only a riveted fit but it is possible to seal this area if needed. The plumber will fit an elbow and connect a horizontal pipe to it. Nevertheless, the short length of 100 mm DWV pipe and the elbow’s free flow shape will allow the water to divert ok even with the small head. A 100 mm DWV elbow however consumes 200 mm of depth and this might be all the available head that you have. There must be room available to fit the elbow. You will also need some slope but this needn’t be much. WET SYSTEM DIVERSION FROM THE HOUSE You need to have a wet system. Wet systems should have mosquito proof leaf diverters but while they are mandatory in many areas, in many areas they are not. You will not have the available head needed to fit leaf diverters unless the tank’s top meshed inlet is lower than the tank’s roof. If you have leaf diverters fitted, then you can have a tee fitting rather than an elbow at the base of the riser. This then allows you to fit a reducer to the additional opening so that you can divert a smaller flexible pipe to a small inlet valve about 100-200 mm above the bottom of the tank. The small inlet pipe will operate with a variable higher head pressure than the riser as the head pressure will be determined by the height of the water in the tank. This gives the small pipe priority flow which has the following advantages: • Assists the riser during peak flows. • Gives the bed load a low resistance higher velocity flow path into the tank, flushing the wet system every time it rains. • Increases yield by reducing the need to flush the wet system. • Oxygenates the anaerobic zone, improving water quality. All of these lessons were learnt during the development of our Supadiverta program. Having the riser above the tank further reduces head. If the top meshed inlet is 2.4 m, the available head could be 150 mm at best. The 10 metre distance between the tank and the house needs to be calculated to allow for the total pipe length plus an allowance as additional pipe length made for fittings. A 150 mm head won’t cut it during heavy rain. I will address the wet system and answer some other matters once you confirm the tank’s inlet height. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Simple water tank design 3Feb 17, 2014 6:46 pm First of all, thank you for a fantastic reply. The information that you have provided here to me and others is invaluable! I've taken all that you've said on board. I'll comment on the areas I have questions/comments about or answers to your questions. We think we'll use just a little over 300 liters of water a day. But we don't have any usage data to back that up. We've been living, frugally, on a very small tank, fed by a very small roof for the last year. I'd say less and 1/3 of the catchment we'll have with the new house/shed. I think outdoor demand should be near zero since we plan to have a dam and run water from that for the garden. The guy we are buying the tanks from said first flush diverters don't have a cost in terms of head. But I guess he was not talking about manually operated ones? I don't think we have much room to play with in terms of head from house roof to tank. I'm willing to route the water from the diverters somewhere useful and have it arrive as it falls (perhaps a small pond) but I'd rather use one where I can control the water usage if I can. I haven't checked fire fighter requirements. I'll ask the tank people to provide it fitted for the firemen. I'll ask that tank 2 be setup with inlet near the bottom. I'm assuming a check valve near the pump stops tank 2 emptying and is probably necessary even if the water goes in the top of tank 2? I had planned (clearly without much thought) to address the emergency case of needing water back in tank 1 (fire for example) by simply running water back down the up line, but if there is a check valve then thats not so easy. Perhaps a check value bypass? or a "short" between the down pipe and the up pipe before the check valve? I'm not sure how the shed roof will be connected. It is a gabled roof. 90 sqm. 2 X 15 m gutters on the side. Tank near the one gabled end of the shed. The house is a skillion roof with one long 20 m gutter. Head: Tanks are flat on top, the gravel pad is inset into the ground, so they will sit at ground level. The inlet is about 10mm above the top of the tank. The tanks are 2.34m tall. Its about 10m from the house to tank 1. I now think the gutters are more like 2.8m from the ground on the house. So: 2.8m high gutter - (2.34 high tank + 0.01 thickness of inlet cowl + 0.1m gravel - 0.1m inset hole for gravel) would seem to give about 40 cm to play with for pipe losses and first flow diverter? How much does the supadiverta cost in terms of head loss? cheers, tas Re: Simple water tank design 4Feb 19, 2014 6:14 pm 300 L per day usage is 109,500 litres annually. July to October are your wettest months and your rainfall pattern is consistent. Your new tanks could/should fill over winter. 34,000 L (+ 10,000 L fire fighting storage compartment) is not a lot of storage capacity but it will last you over 3 months with no rain. I would usually suggest having more storage but you might need to start deciding long term where the excess will go and how it will get there. You might have to branch off the house supply pipe to provide an emergency supply back to tank 1. Maybe branch to a tap at tank 1. FIRST FLUSH DIVERTERS A dry system FFD doesn't lose head as it is just a Tee drop off a horizontal pipe. A wet system is different unless the FFD is directly under the pop and the wet system branches horizontally off the FFD via a tee and then vertically via a 90 degree elbow so that the wet pipe drops parallel with the FFD. FFDs are a mixed bag. If you have overhanging trees and possums, they are essential. However, most FFDs are too small. Let's use the shed as an example. A FFD should drain a minimum .5 mm of rain every rain event but preferably 2 mm after a dry spell. Your shed has two 45 sq m roof sections 90 mm PVC stormwater pipe is measured as an outside diameter (OD), the 86.2 mm inside diameter (ID) gives a volume of 5.84 litres per metre. Most places use 90 mm FFDs and diverting the first .5 mm off a 45 sq m roof area would require a 90 mm FFD nearly 4 metres long! .5 mm (22.5 litres) isn't much water to wash a 45 sq m roof. If it is 2 m long, you are trying to wash the roof and flush the gutters with ¼ mm of rain! The stronger 100 mm (SN6) DWV pipe has an ID of 104.2 mm, giving it a volume of 8.53 litres per metre, 46% greater than the 90 mm stormwater pipe. Most muck is washed from the gutters during heavy rain, usually after the FFD is full. The dripper that most FFDs are fitted with discharges much more water than the diverter’s volume. By way of example, one drip per second (not Apothecaries’ measure) is about 13.5 litres per day. How much water do you think the dripper shown at 3:16 in the video below would waste in a day? And that is only one downpipe! http://www.youtube.com/watch?v=N0S5zTcz0FY WHY THE FFD BALL FLOAT? The ball float in most commercial FFDs is claimed to stop a Venturi effect from recycling the first flush. In reality, the diverted water settles in the flush pipe and any Venturi effect is negligible. When the FFD is full, the ball actually helps solids pass over the flush opening due to the ball’s shape altering the flow pattern. Our research has shown that having an unsealed first flush pipe is more beneficial as the bed load can then fall down the pipe throughout the entire rain event. SHED You only need one 90 mm stormwater pipe on each side. These can connect at a tee next to the tank and then have one pipe going to the tank. The most efficient position to have the pops is midway along the gutters. I wouldn’t have the pop at the end of a 15 m gutter but 2/3 of the way along would be fine. You have plenty of head but not quite enough to fit leaf diverters. A FFD could be fitted directly under the pop with a tee. Place some shade cloth over the tank’s top meshed inlet to make debris removal easier. HOUSE AND WET SYSTEM The head is critical. You must also add a minimum head loss allowance of 25 mm (for your climate and roof area) to compensate for the height of the water pushed above the top of the vertical riser during a 1:20 ARI, remembering that the water doesn’t flow out paper thin during a storm. If the gutter is in fact 2.8 m and the tank is 2.35 m to the top of the inlet cowl, you might still have a head close to 400 mm to play with after other head deductions. The 150 sq m roof will likely need 3 downpipes for compliance (depending on the gutter's cross sectional area and downpipe size) but if they are lax on compliance, your straight 20 m gutter can easily be serviced by two well placed 100 mm downpipes and a suitable well sloped gutter. Avoid having downpipes at the end of walls. The wet system can be substantially improved if leaf diverters, a sediment trap and a low restriction inlet are fitted. You cannot fit a low restriction inlet if you don’t have sealed mosquito proof leaf diverters. 9.4 VERMIN AND INSECT-PROOF SCREEN 9.4.1 General The Australian Guidelines for Water Recycling—2B specify that inflows and overflows from above-ground tanks and vents have to be provided with a securely fastened vermin and insect-proof screen mesh with holes less than 1.0 mm in diameter or as defined by the local responsible regulatory authority. It is possible to fit leaf diverters to eaves in most situations. If you can mount leaf diverters under the gutter and have short pops draining to them with a suitable clearance between the pop and the mesh, then it could be possible to still have leaf diverters and about 200 mm head. This low head is normally unacceptable but the tank is close to the house and the following would apply... You are in a low rainfall intensity zone and the house 150 sq m roof area would generate a little over 300 L/min during a 1:20 ARI. You would use a 100 mm DWV pipe. Having a sealed mosquito proof leaf diverter allows you to fit a low restriction inlet about 150 mm above the bottom of the tank. This would be supplied by a reduced pipe coming off a tee at the bottom of the vertical riser. A Pondflex hose would be used between the pipe and the low restriction inlet. I suggest fitting a 40 mm inlet. I will post a photo of the fittings in the next few days when I find the time. The low inlet will do the following (some info already posted in earlier post)... Operate with greater head as the tank’s (variable) water level is below the tank's overflow pipe, not the top of the riser. Allows a lesser head by supplementing the flow rate. Operating with more head than the riser gives the low inlet priority flow. Water would only discharge from the riser during heavy rain. Flush the wet system every time it rains, leaving fresh water retained in the pipes between rain events. This improves water quality. Oxygenate the tank’s lower levels, improving water quality. Balance the retained wet system water level to the height of the tank’s water level. This leaves less water in exposed pipework. SEDIMENT TRAP A simple sediment trap can be fitted to a non turbulent section of wet system pipe to capture most of the bed load. This is made by fitting a 45 degree junction to the pipe. The junction’s branch faces downward and the slow moving bed load simply falls down the bottom opening. The branch is size reduced and regularly flushed. Little water is lost. I will post a diagram or photo later. Virtually no sediment will enter the tank from the house catchment. Re the Supadiverta, depending on how it was fitted,you would lose between 280 mm and 600 mm head because it is also a leaf diverter but this is offset by a head gain due to the water in the tank obviously always being lower than the top of the vertical riser plus there is less friction loss along the pipe itself. The Supadiverta can be fitted with either (nominal) 20mm or 25mm pvc pressure pipes at the outlets and the 25mm pipes can adapt to 40mm DWV pipes which can then be upsized as more downpipes drain to the sub surface carrier pipe. The Supadiverta is however more suited to suburban homes that want to harvest multiple downpipes and/or eliminate the tank's overflow pipe when siting a large tank away from the house as opposed to a property needing to collect every possible drop. I don't think that it would suit your situation but the research and development program has resulted in the wet system methods discussed here that are now benefiting others in Australia and overseas by improving the water quality, increasing yield and reducing maintenance. EDIT: Bonus points questions. tasman Bonus points for answers to: How do tell how much water is in tank 1? There are several level gauges available including ones that can transmit data to your computer. If you get a basic one, obviously you would need to see it from a distance. It depends on what you want and what you want to spend. You can also get water meters to measure usage. Have a read of Munter's very good blog to see where he got his and what he paid: http://renovations08.blogspot.com.au/20 ... using.html tasman Is it easy to attach a float cutoff valve to tank 2 and set a pressure switch at the pump such that it stops pumping when tank 2 is full? Any inline valve is a flow restriction. That aside, you could consider a low pressure Topaz valve but check first with the tank manufacturer re fitting and the tank's warranty. http://www.youtube.com/watch?v=fdn12zYKNmI http://www.jobevalves.com/webapps/i/86738/203450/304724 Personally, I would use a simple timer. You will soon get to know your tanks and pump. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. 18 90417 From what I know about water tanks (I've been working with a client on them for a few years now) is this - The concrete can last a lifetime if they don't crack for some… 2 10618 If you can calculate the reasonable charged head from let's say 100mm below the gutter to the top of where the vertical riser's horizontal discharge pipe will be, that… 11 17524 |