Browse Forums General Discussion Re: Queries on Rainwater Harvesting 4Oct 01, 2023 1:30 pm There is a whole lot more to know than just the answers you seek but they are a good start. ![]() 1) Any tips on calculating storage tank size? It is important to consider several factors:
Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ ![]() 2) Does the "system" somehow connects back to mains? Not always, it depends on the intended use. See above. If intending to plumb to the house mains water line for potable uses such as drinking, cooking and even bathing, the water must be drinking water quality. Fitting a backflow prevention valve to the mains water system is mandatory when connecting an above ground rainwater tank to the house mains water line. If it is a buried rainwater tank, the anti-backflow valve must be a testable device. Some regions foolishly only allow automatic mains water switching devices to service cisterns but this is often ignored and a much cheaper manual system installed instead. ![]() 3) Is it recommended to install a filter to rainwater harvesting system? If the rainwater harvesting system is designed for best practice, good quality water will be diverted to the tank and the best quality water in the tank will be delivered to the pump. Best practice includes using a properly positioned (most are not) first flush diverter, a charged system sediment trap and a good floating intake filter. Before deciding on added filtration, the rainwater should be lab tested with the sample taken from the tap. An appropriate filtration system can then be selected for the harvested rainwaters' intended use. ![]() 4) Generally, always full or empty? Don't be disappointed to have empty tanks if you are harvesting and using a lot of rainwater. ![]() 5) What kind of maintenance is required in total? Overflow outlets have a mosquito proof mesh. These are a flow restriction that often clog up, causing tanks to overtop. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ To access the mesh from inside the tank, the tank's top inlet's meshed basket must be fitted within arms reach of the mesh. If it isn't, you have to remove the overflow pipe to scrub it but you won't be cleaning the mesh face! It is stated in the Plumbing Code of Australia (PCA) which is Part 3 of the National Construction Code (NCC) that rainwater storage must allow access for cleaning and maintenance. It is best to not have any mesh fitted at the outlet but instead fit an Air Gap made by Rainharvesting to the overflow pipe. This is a very good inexpensive product that has two easily serviced mosquito proof filters. Removing the mosquito proof mesh from the outlet also increases the tank's overflow discharge capacity 10-15% when the mesh is clean but by much more if the mesh is dirty. https://rainharvesting.com.au/products/ ... s/air-gap/ Wet system/charged pipes build up sediment, particularly in the pipes furthest from the tank because rainwater tank installers most often annex the house stormwater pipes. Subsurface stormwater pipes are designed for a 1:100 year storm event because they also need to collect surface drainage and collect water from silt pits that ag pipes etc drain to. In short, annexed stormwater pipes at the head of a rainwater harvesting system are too large to ever attain an adequate sediment flushing velocity. If building, be aware that having the stormwater pipes annexed for rainwater diversion pipes robs you of your surface drainage options unless you install more pipes. A large volume of water with no air interface is also retained in the pipes between rain events. Water retained in a wet system is invariably of poor quality which flows into the tank the next time it rains Wet systems should incorporate good mosquito proof leaf diverters fitted to all harvested downpipes and also be fitted with flushable sediment traps. Tank Designs and how they are optioned is often poor. Things to avoid are- Low outlet valve. A low fitted valve is a drain valve but it is what most homeowners have their pump connected to! Unless you have a floating intake filter, option the pump's draw valve so it is 100 mm above the bottom of the tank at the valves lowest point. Rainwater settles in stratified layers with the lowest oxygen, highest density (dirtiest) water settling in the bottom of the tank. This is called the anaerobic zone. Position of tank's top meshed inlet in relation to the tank's valve that supplies the pump. Water falling into a tank near to the side wall where the tank's outlet valve is fitted will stir up the sediment layer close to the valve. Turbidity can last for several days and is often the cause of complaints. Submersible pump Submersible pumps are quieter and the outside area is aesthetically more pleasing but many are simply placed on the tank's floor. If they draw water in from the bottom, they spend their life vacuuming the sediment layer and also supplying the worst quality water in the tank. Submersible pumps that draw water from the bottom must be located on a raised base above the sediment layer. Submersible pumps should not be positioned in the tank with the inflowing water falling directly above it but it is nevertheless common. Overflow pipe position. There is a trend to design tanks with the overflow pipes fitted to the tank's roof, An overflow pipe drains faster with increasing heights of water above a horizontal outlet's invert or a vertical intake's (internal upturned elbow) crest but many tanks now have little mitigation capacity above the outlet's obvert. Note in the photo below how the overflow pipe's mesh cannot be accessed for cleaning and how easily mosquitoes can access the standing water in the vertical riser. From egg to adult mosquito takes 12-14 days! Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ First Flush diverter position. First flush diverters are most often errantly installed at the top of vertical risers. Monkey see...monkey do! Think about it! Where does the first flush (polluted roof wash) first go? Into the downpipe of course! What does a first flush diverter fitted to the top of a vertical riser fill with? The settled water in the vertical riser of course! Also note in the photo below the lack of mitigation above the overflow outlet's obvert. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Submersible pumps. If the pump's inflow is at ground level (see red arrows below), the pump must be on a raised platform. If not, it will spend its shortened life vacuuming the tank's floor. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ External pressure pumps. Do not connect a 90 degree elbow directly to the pump's suction port. Have the suction hose respect at least 8 straight lengths of internal diameter immediately before the pump's suction port. Use the correct size internal diameter hose to match the pump's suction port size. The commonly used 25mm Blue Stripe poly pipe has an internal diameter of just 21mm! Proper pump size. If only using a pump for laundry and cistern supply, you do not need a large expensive pump because cisterns and washing machines are slow fill, short duration end fixtures. Also fitting a good size pressure tank will save energy costs, substantially prolong the pump's life and eliminate any potential water hammer issues. Because rainwater is pure, it will absorb the plasticisers found in many cheaper pressure tank bladders and diaphragms, causing them to become brittle and fail. Only buy pressure tanks that use butyl bladders and diaphragms. Also, don't strangle the pump supply by using small diameter pipe/hose. Automatic Mains Water Switching Device. I strongly recommend using a hydraulically operated (no electricity) automatic Acquasaver valve rather than any other automatic type. A bonus is that the Acquasaver is also reasonably priced but be aware that they come in two sizes, 3/4" and 1". https://asctanks.com.au/product/aquasav ... OYQAvD_BwE Designing to best practice will harvest and deliver a better quality resource, substantially reduce maintenance and is most often cheaper. 3in1 Supadiverta. Rainwater Harvesting Best Practice using siphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost, siphonic, eaves gutter overflow solution. Grate, thank you! RexChan if thats the reason i could sleep well without thinking about additional cost. But 1st i'll need to read about NRV cleaning/replaing stuff. I… 7 33193 That was always going to be a challenge and a test of patience. Full marks to your mate. Did you discuss the wet area near the trampoline? 16 20332 ![]() |