Browse Forums Eco Living 1 Jan 28, 2013 6:44 pm [vimeOur build will be commencing soon so we are finalising the associated bits & peices, one being the water tanks. We are installing a big tank 40,000ltrs behind the garage which is about 50mtrs from the house. It has been suggested a smaller feeder tank closer to the house that when the level drops to pre-determined level water will pump from the big tank to the smaller one. The reason being when using small amounts of water washing hands, filling kettle etc less wear & tear on the pump. Does anyone opperate a system like this? or suggestions on what else to consider. Many thanks, o][/vimeo] Gandj Re: Do we need a smaller water tank next to the house? 2Jan 28, 2013 7:26 pm A small tank near the house will only work if you can raise it to a high enough level to give you reasonable pressure. A better solution, in my opinion, is have a pump with a pressure tank. The link below explains how it works. http://www.apswater.com/article.asp?id= ... e_problems I think the web site is a bit hopeful saying you can use these for an emergency supply as a typical tank can only supply 10-20 litres before the pump needs to start. The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: Do we need a smaller water tank next to the house? 3Jan 28, 2013 8:49 pm Hi Gandj, You probably don't realise it but your couple of questions raise a number of issues. Without doubt, I could advise you of ways to save thousands of dollars and avoid having a sub standard system. First, a few questions. A 40,000 litre tank implies that you have an irregular rainfall. Are you in QLD or northern NSW. Do you intend harvesting your entire roof area and what is the roof plan area. How many and what size downpipes will you have? Is there a slope from the house to the back of the garage? How high is the tank's top meshed inlet and how high are the house gutters? The thread's title asks about a small water tank at the house but your question indicates that you actually mean a pressure tank. Is this correct? Is the house single story? Will you also be on mains water? 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: Do we need a smaller water tank next to the house? 4Jan 28, 2013 9:35 pm Thanks for the replies, we live in SA, building in the Barossa. we plan to be as self sufficent as we can in order to keep our living cost down having recently retired. The house has 8 down pipes and 6 off the shed & carport. Our block slopes right to left and front to back, where the tank will be sited it is at least 1mtr lower than the house perhaps more. I do not have any details on the tank as yet as we are still deciding whether to get 2 X 22500 or 1X 45,000. The house is a single story, we have mains water on site if required. We had not heard of a presure tank, thanks for the link, any suggestions greatly appreciated as we are on a steep learning curve at the moment Gandj Re: Do we need a smaller water tank next to the house? 5Jan 31, 2013 1:51 am Hi Gandj, Please excuse this late reply but I am snowed under with work at the moment. Here is an overview as to your situation. CATCHMENT: I guesstimate your total roof (plan) area to be about 470 square metres. The Barossa average annual rainfall is about 520 mm, giving you a total of about 245,000 litres per year. The formula is 1 mm on 1 sq m = 1 litre. You will not harvest this amount as there will be evaporation and other losses. A very good system will have a yield of about 85%, reducing your annual harvest to about 208,000 litres. Evaporation from short duration showers and (highly efficient) first flush diversion comprise most of these losses but flush devices fitted with drippers can reduce the annual yield to 70% or less. December to February is your driest quarter with a long term average of just over 60 mm but yield losses will also be higher due to evaporation during light or intermittent rainfall at this time of the year. STORAGE: I suggest that you have two tanks. I also suggest that you read this thread: viewtopic.php?f=35&t=60317 A lot depends on your intended indoor/outdoor usage but with this system, you will have a high yield and divert better quality water to a dedicated house tank. The yield should be in excess of 90%. Flow rates involve hydraulic calculations but you will need to have all downpipes connecting to two 100 mm DWV pipes that would feed to the tanks exactly the same way as the last diagram shows in the above linked thread except that the smaller pipes would be less than the 50 mm diameter shown in the diagram due to your different weather pattern. I think that 25 mm would suffice for your weather pattern and the roof harvest area as the smaller pipe operating with more head than the 100 mm riser will have a sufficient flow rate to flush the wet system during the initial rainfall. The calculated flush pipe size needs to be factored on the available head etc and so the 25 mm I have tentatively suggested could be too small. The (B grade) tank fed by the small flush pipes would be for outdoor and sanitary flushing use only and the A grade water tank would supply the house. The B tank would require a separate small pump for sanitary flushing. The B tank infeed valves can be closed during an extended rainfall period to transfer all inflow to the dedicated house tank as you should try to keep that tank as full as possible but you will get to know the % use from each tank. Toilets usually account for about 20% of household use. TOILET Many people have large pumps to supply toilets but it is unnecessary as cisterns fill slowly. To reduce the flow restriction, the cistern is best fitted with a Fluidmaster 400UK073 cistern valve optioned with the very low pressure 242LP071 seal. The plastic pigs tail flow restrictor should also be removed from the valve's shank. Standard cistern valve seals are designed for high pressure mains water but I have used the low pressure seal with a hybrid mains and pump system at my place for many years without any problems. http://www.haron.com.au/fluidmaster_products.html REGULATIONS: I am not in S.A. and you will need to check the regulations as they do vary between States. The Plumbing Code however requires that an automatic or manual mains water switching device is fitted when a water tank is connected to a toilet also supplied by mains water. I started a thread about this as I have seen many people who have been ripped off by 'professionals' not giving the correct advice. Many people end up paying nearly $1,000 and sometimes more for an oversized pump and automatic mains make up device they do not need. viewtopic.php?f=35&t=61491 viewtopic.php?f=35&t=61588 DO NOT allow the plumber to use and bury 90 mm stormwater pipe, make sure that they use 100 mm PVC pipes, preferably DWV. The 90 mm pipe is thin walled and only holds 5.8 litres per metre (the Inside Diameter (ID) is 86 mm) whereas the 100 mm DWV has an ID of 104 mm and holds 8.5 litres per metre. You will need this pipe capacity if you have just the two wet system infeed pipes. The two 100 mm pipes will preferably need a hydraulic flow capacity that I always design to handle 1.5 times the region's 1:20 Average Recurrence Interval (ARI) - otherwise known as a 1 in 20 year storm event. You area's 1:20 ARI is most probably 120 mm per hour. The ARI is worked out over a 5 minute rainfall intensity and so this translates to an average of 2 mm per minute for 5 minutes. For your system, I would recommend an inflow capacity of 3 mm per minute for 5 minutes when the tanks are full. The pipes will need to drain quite some distance to the tanks. As the harvesting system has to travel for a good distance underground and remains full of water after it stops raining, it is known as a wet or charged system. This means that you should also have mosquito proof leaf diverters fitted to the top of every downpipe to deflect larger debris. Leaf diverters also allow the downpipes to overflow excess water at the leaf diverter and not flood the gutter during a severe storm. Wet systems should never be installed without an air gap in the downpipe for this reason but this is just one of many essentials that have not been regulated in many areas. Note that there are also no regulations for determining hydraulic flow capacities to water tanks and the regulations or lack of are a disgrace. You will need to advise your builder and plumber as to how you want it done. My recommendation that you design for a flow capacity that is 50% greater than your area's 1:20 ARI is the way I do it, it is not a regulation. BALANCE LINE: This would need to be a flexible coupling (usually 90 mm) set high between both tanks. I would not use a low primary balance line for your install as the water quality will be distinctively different between the two tanks but a smaller one could be fitted 150-200 mm above the bottom for emergency transfer. The best quality water is always near the top. TANK OVERFLOW: The tank's overflow MUST be equal to or greater than the inflow capacity. Few regulations state this. You could possibly have nearly 1,000 litres per minute flowing to your tanks during a 1:20 ARI. Your overflows will need to handle this. Most tanks also have some mitigation capacity that aids the overflows. The first linked thread originally considered having two Tankvacs fitted. A Tankvac fitted to the dedicated house tank would be ideal as this tank would receive most of the inflow during a storm but would also overflow/balance to the B grade tank. The B grade tank would only need fitting with a normal overflow pipe. The tank's design would need to be examined before this suggestion was implemented. 1. Tankvacs generate syphonic flow and drain at about 9 litres per second once the 80 mm overflow pipe is primed. 2. Tankvacs are fitted with suction pipes that vacuum the tank's floor when overflowing. This removes sediment and takes the worst quality water from the anaerobic zone, considerably improving water quality. http://www.tankvac.co.nz/ OPTIONING THE TANKS: The two additional flush inlets (probably 25 mm for your rainfall pattern and anticipated head) should be fitted about 150-200 mm above the bottom of your tank at their lowest point. They should also be fitted no more than 60 degrees from the outlet that feeds the pump. The pump draw outlet should also be fitted a minimum of 100 mm above the bottom of the tank at the lowest point. The inlets less restrictive flow path and greater head allow the wet system pipes to be flushed into the B grade tank every time it rains. Normal wet systems have to feed to a tank's top inlet via a vertical riser that goes up the side of the tank. Unless there is very heavy rainfall, there will be insufficient velocity to flush sediment and decaying organic matter from the underground pipes. Having the lower inlets provides a much less restrictive flow path. The necessity to regularly flush/drain standard wet system pipes wastes a lot of water. With your house and shed as described, you could possibly have +100 metres of 100 mm DWV pipe holding over 800 litres of water between rainfall. Having each pipe fitted with a vertical riser to supply the house tank and then reduce the horizontal section to 25 mm to feed to the B grade tank will ensure that clean water goes to the A grade tank during heavier rainfall plus the water that remains in the wet system when it stops raining will be cleaner and free of debris. As I don't know the levels, tank and gutter heights etc, I can only give an overview at this stage. SEDIMENT TRAPS: Also have a look at the sediment trap that is discussed in the other thread. This is DIY, easy to fit and will get rid of a lot of the bed load with little loss of water. PRESSURE TANK: This will also be in the other thread's summary. Given the distance between the house and the tank, you might want to consider a good sized pressure tank. There will be a lot of friction loss if you pump the water 40 metres to the house. 25 mm Blue Line poly pipe is mostly used but this is OD, the ID is usually about 20 mm. Supplying a pressure tank at the house is a good option. If you pump water to a smaller tank at the house as you have been advised by others to do, you will still need to pump water from that small tank. You are better off buying a pressure tank. PUMP: The B grade tank will need a separate pump but there are some good ones available at good prices. This is also discussed on the other thread. ALTERNATIVES: You have no choice but to use a wet system. A standard wet system will: Have less available head. Accumulate debris in the wet pipes. Require flushing to purge debris and prevent stagnation. Provide water of a lesser quality. Require 14 first flush diverters, i.e. additional expense and considerable yield loss. Standard wet systems are sub standard and I could not recommend that you have one. EDIT 31-05-13 Most first flush diverters have a dripper that drains at approximately 4 lph and during intermittent rainfall (which is usual), the flush chamber serves as a reservoir to continue this supply and when it resumes raining, the chamber is topped up. During a 24 hour rain period, a dripper can drain nearly 100 litres plus the volume of the flush chamber when it finishes raining. This is a lot of water lost through 14 first flush diverters. When you work out your annual yield loss, you will see why it is best to try and capture this water. 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: Do we need a smaller water tank next to the house? 6Feb 01, 2013 5:23 pm SaveH20, Thank you for your very length and informative post this has re-inforced some of the information I had already read. This is one the great things about this forum, people who freely give their time to offer advice & solutions to others, very much appreciated, Gandj 18 90484 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 10632 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 17530 |