Browse Forums Eco Living 1 Sep 20, 2013 8:54 am Hey folks, We're about to move through the signing of a contract with a custom builder in country WA. At this point I have house plans in draft format which I'll share when I can a) host them and b) remove our name from them (minor technical details I'm sure!). Basically we have a long rectangular house on a block with some slope. The house is to be roofed in zincalume, and we've requested that all the roof water be captured and sent through to a rainwater tank. We have also requested grey water separation from the septic system. The rainwater tank is to be supplied by ourselves (and the pump, and any grey water system parts beyond piping), the house is surrounded by about 1m of concrete all the way around. The rainwater tank will be situation past this 1m of path, past the carport on the western side of the house (that's the low end of the slope). I'm thinking we need to say more in the contract than "provision a rainwater collection system" and "provision a grey water collection piping" to get what we want? (And "provision rainwater taps in kitchen and on outside of hours") What I want: Rainwater tank Electrical cabling for the water pump to be underground/concrete to the water tank. (I am assuming the water pump will sit alongside the tank) ALL the rainwater for ALL the roof (including carport) to divert through this system and feed into the tank. I will install additional overflow management as needed. (A wet system?) (I'm concerned they'll just capture a small area) Easy access to clean filters and maintain the system. The tank stand to be done in the earth/site works. (We're looking at needing to level ground for a 20k-50k litre tank) Total roof area is approx 240m2 including eaves. (House is 23mX8m(ish) plus alfresco, concrete surrounds, eaves, carport etc) Piping for the water to come back into the house to be concealed under concrete. Appropriate taps as agreed. Greywater (all our waste plumbing is already along one wall at the rear of the house) Easy separation of the water at a turn valve? point - so I can manually divert it to either the septic or out through a second set of pipes to an agreed exit point (happy to negotiate dependent on site works where this point is). (I plan to then install a grey water holding tank and management system down the (fairly short/quick) track.) Are these assumed in the contract or should I be very specific? What are other people's experience of this stuff. For what it's worth - the builder pulled a small face when I asked for this stuff but indicated he knew exactly what I was asking for and indicated it'd be about $1k for each thing - rainwater collection, rainwater taps, grey water diversion - $3k all up and then willingly put it in. I have yet to see the contract to confirm but it's in the quote so I assume it's come in at about that. Re: Rainwater collection - pre build prep and contract advic 2Sep 21, 2013 8:05 pm Hi snuck, Firstly, thank you for your comprehensive opening post. It makes it easier to respond. I would fit a 2 way diverter to the outside laundry pipe so that you can separate the washing machine's final rinse as this water is of reasonable quality. You have posted that the water tank is to be plumbed into the house. Are you are dependent on harvested rainwater for potable use as you have said that you want filters? If you are on the water grid, then I assume that you will only connect to the toilets, laundry and the HWS provided that you can harvest enough water to supply same. Different plumbing regulations apply to each situation and the regulations also vary from State to State. The first thing to do is check what your area's average annual rainfall and your 1:20 Average Recurrence Interval (ARI) is. The 1:20 ARI and the roof areas harvested determines the eaves gutter and stormwater pipe size for compliance and the average rainfall and the frequency will determine your best tank size. A 1:20 ARI is based on a 5 minute rain intensity but it is given as a 1 hour duration. For example, Melbourne's 1:20 ARI is shown as 130 mm/hr and this equates to a 5 minute intensity with an average of 2.166 mm/min. I can give your 1:20 ARI figure if I know your region. The information is needed for the rain harvesting system's hydraulic design. 1mm of water on 1 sq metre = 1 litre. As you are in country WA, I will use a figure of 120 mm/hr (an average of 2 mm/min) as an example. If applicable,this would mean that your tank would receive an average 2 mm/min off your 240 sq m roof harvest area (480 litres per minute) during a 1:20 ARI. I always design the pipe size and required head for a bit more than this as a safety margin, sometimes up to 50% more. As the tank will be away from the house, you will have a "wet system". A wet system is where the downpipes connect to a sealed underground storm water pipe that is plumbed to the tank. At the tank, the pipe is plumbed vertically up the tank's wall and then a short horizontal distance to the tank's top meshed inlet. It is called a wet system because it retains water during rain periods unless drained. The problem with wet systems is that the velocity of the water is usually inadequate to flush a lot of detritus up the vertical riser. For example, if a 100 mm DWV (Drain Waste Vent) SN6 pipe is used, the internal diameter is 104.2 mm, giving a volume of 8.53 litres per metre. A horizontal flushing velocity of .6 metres per second (5.12 litres per second or 307 litres per minute) is a minimum recommendation but the vertical riser is not horizontal!!! Wet systems are fitted with flush valves so that the pipes are regularly flushed of contaminants and while this prevents stagnation, it is wasteful. The number of below ground horizontal wet system pipes and their size will depend on the friction losses (pipe length + maximum required flow rate + fitting losses) and the hydraulic head. A 100 mm DWV pipe with a 500 mm head and (guesstimating the length at this stage) 80 metres of (total) friction loss will flow at about 420 litres per minute; i.e. too slow for your system. A low restriction branch line (see below) will supplement this flow rate but will a 500 mm head be available? If not, then two 100 mm or a single 150 mm DWV pipe will be needed. All this is easily worked out once the actual head and friction losses are known. To improve the water quality and yield, a tee fitting should be fitted at the vertical riser's base instead of an elbow. The additional branch is then reduced in size (usually to 40 mm) and the additional branch/pipe provides a low restriction flow path to an inlet fitted about 100-150 mm above the bottom of the tank. This pipe will operate with a greater variable head (that depends on the water level) than the vertical riser that needs to rise to the top of the tank. This ensures that the wet system is constantly flushed as the water will flow through the low inlet except during heavy rain. A bonus is that the low inlet also supplements the overall flow rate. This often eliminates the need for an additional wet pipe. As water must pass through mosquito proof mesh before entering the tank and as the low inlet is a direct entry point, you must have mosquito proof leaf diverters fitted to each downpipe if using a low restriction unmeshed inlet. These are mandatory fittings to downpipes supplying a wet system in many areas of Australia. It is also best to have 2 tanks as this will allow you to have a settling system. A settling system is where all of the water is fed to one tank and the second tank (usually the same height but with a narrower base) receives water from the first tank through a balance line. The pump then draws the water from the second tank. To further improve the transferred water quality, a WaterBoy can be fitted to the larger tank's balance valve so that only the very best quality water is transferred. The second tank does not need to be fitted with an overflow pipe and the overflow outlet can be either capped or not fitted. http://www.crystalclearwater.com.au/waterboy/ I also recommend that a DIY sediment trap is fitted to the horizontal wet system pipe. See the diagram below that is off another thread (also linked). http://imageshack.us/a/img37/3204/sedim ... tflush.jpg viewtopic.php?f=35&t=60317 The trap is fitted to a non turbulent section along the wet system. Bed load travels very slowly and when it reaches the opening, it simply falls down. Because the pipe reduces in size, flushing wastes little water. Because your tank will have the potential to receive about 480 litres per minute during a 1:20 ARI, a standard 90 mm or 100 mm overflow pipe will not cope. I strongly suggest that you have a TankVac overflow system fitted. http://www.youtube.com/watch?v=e1_B9WITe94 TankVac is a syphonic system that vacuums sediment and the worst quality water through a network of smaller pipes on the tank's base. It overflows at 9 litres per second (540 lpm) through an 80 mm DWV pipe that drains into a larger outside drain pipe. A vacuum break inside the tank prevents the tank from syphoning dry. The Australian contact is Neale at namcpheeplumbing@hotmail.com Using a large pressure tank will substantially reduce the number of pump start/stops and allow the pump to operate at peak efficiency. The (U.S.) link below explains how they work. http://www.sprinklerwarehouse.com/DIY-P ... s/7024.htm If you incorporate these simple designs, you will have the best quality tank water in the district. EDITED: Removed link. 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: Rainwater collection - pre build prep and contract advic 3Sep 22, 2013 6:50 pm Thanks H20! Sorry about the delay in reply - spotty internet for some reason. I'll be taking this to the builder.... We're planning to use the rainwater initially purely for drinking, and piping mains water through the rest of the house. Eventually we'll go to a full rainwater supply situation, but only when we get enough roof to collect enough rain (or we'll put a switch over of some kind in so we can pick and choose which water supply when, but it will be all or just kitchen tap if/when we do that). We get an average rainfall of 360mm where we are (http://www.bom.gov.au/climate/averages/ ... 0035.shtml) with just a few days each year (less than 10) of 20mm+ rainfall - so it's going to be a challenge to go offgrid without getting into some serious water harvesting. We have other rain water options, but for now we'll be happy with good quality drinking water and access to water whenever the pipeline goes down (which it does in our current hometown - not the one we're building in - reasonably often - new town is on the Kal. pipeline so it should be better!). Re: Rainwater collection - pre build prep and contract advic 4Sep 23, 2013 3:11 pm Re the mains water switching device, the plumbing regulations mandate the use of either automatic or manual devices when rainwater is supplied for sanitary flushing. Manual devices are much cheaper and trouble free. http://www.asctanks.com.au/mainrain-mains-switch-over/ With the chance of mains water supply interruptions, you will probably want the option to also use the harvested water for sanitary flushing when needed. The easiest way to do this is to fit two cistern valves to the cistern, one supplied by the pump and the other supplied by the mains water. To plumb this, you... Have two Fluidmaster 400UK063 cistern valves fitted to the cistern. http://www.haron.com.au/fluidmaster_products.html Remove the plastic 'pig's tail' flow restricter from the bottom of the shank of the cistern valve that will be supplied by the pump. Also remove the standard (mains water pressure) seal from under this valve's top cap and replace it with the optional very low pressure (242LP071) seal. Make sure that the short float arm is kept pushed up when twisting the cap off (as per the instructions). The pump then connects directly to the second cistern valve via AUSPEX pipe. This is easy to install and gives you two isolation valves inside the toilet that qualify as a manual switching device. The cistern valves also have air gaps to prevent cross contamination between the two supplies. See the figure 1 diagram in the link below. http://www.pic.vic.gov.au/__data/assets ... sterns.pdf The low rainfall and weather pattern is a challenge but the annual average rain of 360 mm falling on a 240 sq m roof harvest area equates to 86,400 litres. 1 mm on 1 sq m = 1 litre. The problem is the rainfall pattern. Rainwater harvesting does not have a 100% yield and 85% is considered very good. Evaporation during brief showers, particularly during warmer periods, is a primary cause of yield loss but first flush diverters can also severely affect yield and these can reduce yield to as little as 65%. If we use an 85% yield, this brings the annual average roof harvest back to 73,440 litres or 201 litres per day. The average person drinks about 3 litres per day. http://www.professorshouse.com/Health-B ... ink-a-Day/ This leads to a few variables as to how you want to collect and use the rainwater. For example... FIRST FLUSH DIVERTERS If fitted, the water should be collected and used for garden watering. To do this, the collection chamber needs to be fitted with a manual drain valve at the bottom so that the water can be collected or alternatively, the drain valve can be connected to a poly pipe that also drains other diverters to a small holding tank. Given your location and the need to maximise yield, you might not consider first flush diverters. If you don't have mosquito proof leaf diverters that allow you to fit a low restriction flow path between the wet system and the tank, you will need a flush valve fitted to the wet system pipe at its lowest point so that the wet system pipes can be flushed to prevent stagnation. Wet systems require adequate head pressure. I have checked AS/NZS 3500.3:2003 and your 1:20 ARI appears to be 120mm/hr (an average of 2 mm per minute for a 5 minute duration). That gives your roof area a harvest capacity of 480 litres of rain per minute during a 1:20 ARI. One 100 mm DWV (Drain Waste Vent) pipe with 100 metres of friction loss (pipe's length + fittings friction losses expressed as additional pipe length) with a 1.5 metre head will have a flow capacity of about 670 litres per minute. This would provide a sufficient safety margin for your system if the (guesstimated) example is relative. I can calculate flow rates once the actual head and friction losses are known. A low restriction branch flow path also supplements the flow rate and allows less head, yet another advantage. 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: Rainwater collection - pre build prep and contract advic 5Sep 23, 2013 7:36 pm Thanks H20, It will be interesting to see how much we actually can collect - I'll keep fairly tight records for the first few years and we'll see. Part of the issue is the low number of significant rains (or more... the high number of small rainfalls) - which means you lose a fairly large chunk to flushing each time and don't get a good run off in the dams or a solid download into the tank. I estimated 80,000L in a good year, 60,000 more likely so we're in the same ball park which is nice to know. You have good solid knowledge. Thanks so much for sharing it. The worst thing you can do is sign a building contract without a pre contract review. Over the years many people have come to me with disputes where they just signed… 0 8351 Thank you so much everyone. This all makes a lot of sense. I guess when you talk to a builder who butters up everything to look very polished, you get to start believing… 7 17629 Ideally you would engage a landscaper to give you some insight what they may need in the space to make your vision come to life… 1 13646 |