Hello,
I'm currently building a 75000 L potable rain harvesting system in rural Oregon. Due to many building mistakes (that's a whole other nightmare) I've had to move my (4) 18927 L tanks farther down hill from my house. This has now raised many questions I wasn't originally figuring into the design.
I've been reading the posts here for the last few months as I try and deal with the many questions I have and was hoping some of the experts here could help me with a few of the remaining questions.
Below is my current design setup: (i've tried to keep it metric but excuse me for any mistakes)
- 167 sq.m house with 185 sq.m roof
- 1:20 ARI for this area is about 177 mm in 24 hour period
- (4) 18927 L x 3.65 m high tanks on an 203 mm thick concrete slab
- The tanks and slabs are roughly 122 meters from the house downhill with drop of about 6 - 8
meters. The top of the 3.65 m tank is roughly 2 - 3 meters below the bottom of the gutters.
- This is going to be a dry system. I've glued and buried 76 mm pvc running from each of the 6
downpipes,three on each side of the house.The left and right side of the house converge into a
76 mm DWV Y pipe and then a single 76 mm pipe feeds into a 1.2 m x 305 mm inground diverter
then into the top 76 mm inlet of the 4th tank.
- 4 of the downpipes will have leaf filters connected right below the downspouts
- All 4 tanks are to be connected to each other with the following scenario: Tank 4 fills first
and overflows via a 76 mm connection at the top to tank 3. There will be a water quieter
attached to the bottom of the pipe in tank 3. Tank 3, 2, 1 will be connected by the bottom
inlets via a 50 mm pvc pipe. Tank 1 will be the tank connected to the pump and pressure tank,
it will also have a 100 mm overflow pipe.
- Regardless if I use flexible or rigid pvc at the bottom of the tanks, each tank will have it's
own discharge pipe that will be operated by independent ball valves and will discharge over
the hill in front of the tanks. My thought here is that in the event I need to empty a tank
due to contaminants etc. I want to be able to still access and fill the other tanks. (See
diagram)
Questions:
1. I know it's best to have flexible connections at the base of tanks, but I'm having a heck of
a time trying to find potable, flexible, weather resistant tubing. What do you guys use? If I
were to use 50 mm rigid PVC for the connections they would be on the cement slab, so I
believe the only thing that would break or upset them would be a jolt from the cascadia fault
Oregon is next to.
2. Since the top of my inlet tank is about 2 - 3 meters below my gutters I've figured I should
have enough head pressure to fill the tank?
3. Will the 50 mm pipe connecting tanks 3,2,1 be large enough to accommodate the 76mm inflow
from tank 4?
4. I was planning on having my 450 L pressure tank, pump and pressure switch in the pump house
right next to the tanks. Would it be better to have the pressure tank and pressure switch in
the house which is 122 m up the hill or should I leave the pressure switch next to the pump
and put just the pressure tank in the house?
I'm attaching a hand drawn schematic of my proposed setup. Hopefully it works.
https://www.dropbox.com/s/9u7ivvajqtdw3 ... p.JPG?dl=0
75k L potable system design with a few questions.
Page 1 of 1
The same thread was posted on another forum. To see the replies, go to:
http://www.ata.org.au/forums/topic/46445
http://www.ata.org.au/forums/topic/46445
Hi H20,
I was hoping you would jump in as I've been following many of your posts for the past few months while trying to figure out how to get this system to work. You are knowledge of fluid dynamics and the workings of water systems is very impressive.
Sorry about that I now see many of the people posting here post there as well. I'll work from the other forum.
Thanks guys.
I was hoping you would jump in as I've been following many of your posts for the past few months while trying to figure out how to get this system to work. You are knowledge of fluid dynamics and the workings of water systems is very impressive.
Sorry about that I now see many of the people posting here post there as well. I'll work from the other forum.
Thanks guys.
My 'bro' has replied on the ATA forum, it is pointless to do multiple replies. Homeone is a better forum for posting diagrams, photos etc.
Hi All
I've moved to this forum to continue working through my questions as the ATA forum is not as user friendly with quotes, graphics and pic uploads. The link to the other forum is http://www.ata.org.au/forums/topic/46445
[*] For my balance lines I was thinking of using a product from a company called JM Eagle, 50mm flexible hose. The pipe is for potable water, light weight, super tough, is UV stabilized and good for earthquake zones. They say it will last 100 years, but I won't be around to validate that claim. http://www.jmeagle.com/products/water_s ... sewer.html
[*] Per Diver's advice I will use a 100mm overflow on Tank 4 with a graf overflow siphon, connected to the tank with a multi-tite sealing gasket. Do you forsee any issues with using calming inlet in conjunction with the overflow on tank 4?
I've moved to this forum to continue working through my questions as the ATA forum is not as user friendly with quotes, graphics and pic uploads. The link to the other forum is http://www.ata.org.au/forums/topic/46445
Re the balance lines, rigid couplings should never be used because tanks flex, only use flexible couplings. We always use flexible black corrugated UV stabilised pond hose and most irrigation shops here have it and cut it to the required length. The 32mm hose is my favourite because it's a good size and the larger sizes are less flexible over short distances but the size of course is determined by the inflow capacity during a major rain event.
[*] For my balance lines I was thinking of using a product from a company called JM Eagle, 50mm flexible hose. The pipe is for potable water, light weight, super tough, is UV stabilized and good for earthquake zones. They say it will last 100 years, but I won't be around to validate that claim. http://www.jmeagle.com/products/water_s ... sewer.html
I would have a single 100mm overflow on tank 4 and have the overflow elbowed and bell mouthed inside the tank to greatly increase the overflow capacity. The other tanks wouldn't need overflow pipes.
[*] Per Diver's advice I will use a 100mm overflow on Tank 4 with a graf overflow siphon, connected to the tank with a multi-tite sealing gasket. Do you forsee any issues with using calming inlet in conjunction with the overflow on tank 4?
The design primarily depends on your (Oregon) area's 1:10 year return storm event's 5 minute rain intensity. That intensity will be multiplied by 25-30% to bring it in line with our 1:20 ARI to do the system's hydraulic calculations that determine the infeed pipe's maximum flow rate, the overflow pipe size and design as well as the size of the tank's balance lines to cope with a major rain event.
If the water is for potable use, then the hose and pipes should also be suitable for contact with drinking water. It doesn't have to be high pressure hose/pipe because 1 metre (39 inches) of head is only 9.81 kPa or 1.42 psi. The volume or weight of water in the tank is incidental, the pressure only and not the weight relates to the hydraulic head pressure.
We use UV stabilised corrugated pond hose for balance lines when the tanks are reasonably close together because they are flexible. Tanks flex as they fill, see the second photo below.
An internal bell mouthed overflow is shown below. The bellmouth greatly increases the overflow capacity but if you are in a low intensity rain area, it is probably not necessary. Note that the overflow outlet is fitted lower down the tank because of the elbow and the bellmouth's rise.
Two overflows can also be joined to a single vertical overflow pipe, see below.
SUGGESTED DESIGN
Note that I have reversed the inflow and pump tank from your diagram.
All of the inflow diverts to tank 1 and decants through to tank 4. Unless it is a long duration heavy rain event or the tanks are reasonably full, the balance line from tank 3 to tank 4 is usually closed and cracked open several days later. The water that decants to tank 4 will be of very good quality.
Water diverted to a tank must pass through mosquito proof mesh here in Australia and this should apply to all countries.
A settling system provides natural filtration yet it is remarkable the number of multi tank installations that are plumbed with the pump drawing water from the infeed tank!
Rainwater is naturally acidic, it is a good idea to fill a nylon bag with limestone chips and place it in the tank to neutralise acidity. Tether a small buoy to the bag for easy retrieval.
Avoid using copper pipes when using harvested rainwater.
Only one overflow pipe is needed when all of the water is diverted to one tank but the tank's overflow capacity must be greater than the inflow capacity during a major storm event.
Don't have an overflow outlet fitted to the other tanks unless you block it off...remember that the water will rise above the bottom of the tank 1 overflow pipe in order to drain and if the tanks are full, this will cause water to flow from all overflow outlets. We have pvc caps here that fit neatly into the overflow outlet fitting and no doubt they would also be available in the US.
It is strongly preferable to let the water breathe and so the other three top meshed inlets should not be sealed but placing some shade cloth over the mesh will still allow air circulation while preventing sunlight ingress.
Using a tee at the base of the vertical riser allows you to divert an additional pipe away from the tank so that the wet system can be flushed. Being down hill at the lowest point, the additional pipe can also be a length that allows it to be used as a first flush diverter and the first flush manually drained to anywhere you like. First flush diverters with internal filters and a slow dripper are high maintenance and waste yield, having a larger manual drain valve is much better.
In reality, if leaf diverters and a sediment trap are used, the wet system shouldn't need flushing although the line could still be largely flushed through the sediment trap if there was an extended dry period. This then gives the option of fitting a flexible low restriction hose between the Tee fitting and an inlet valve fitted about 100mm above the bottom of the tank. This inlet will have priority flow because the tank's water level will always be lower than the usual height of the water at the top of the vertical riser, giving the inlet more head pressure that the vertical riser. We refer to this additional flow path as a low restriction inlet because the water doesn't have to flow up a vertical riser.
Advantages of having a low restriction inlet includes retaining less water in the wet system, the wet system will be flushed every rain event, the wet system will only retain the last (cleanest) water diverted during the rain event, the oxygen rich water will oxygenate the tank 1 anaerobic zone which improves the water quality PLUS the additional inlet increases the maximum flow rate through the wet system, allowing the use of smaller pipes or compensating for an inadequate hydraulic head.
It should be noted that standard rainwater harvesting systems deliver water to the top of the tank and draw water from the anaerobic zone at the bottom of the tank, the opposite to what is best! To draw water from the cleaner upper levels, you simply install a floating outlet hose to the outlet valve that supplies the pump...see link below.
http://www.crystalclearwater.com.au/waterboy/
A floating outlet hose with an attached fine filter.
We have what we call downpipe wall spacers and these or similar can be used to stabilise the inflow pipe above the tank's top meshed inlet. The photo below shows this fitting as well as a flap valve fitted to the end of the pipe. The flap valve prevents mosquitoes and birds etc from entering the pipe.
The horizontal pipe at the top of the vertical riser must be checked for a downward slope before being secured.
The balance valves between tanks 1 and 2 should be about 100mm above the bottom of the tank at the valves lowest points but the other balance valves can be 60-70mm above the bottom of the tank.
If the tanks are desludged, it is best to remove the tank's top meshed inlet and use a siphon or similar. This is best done when the tanks water levels are high. I have a syphon that I made from 25mm (1") pressure (sch 40) pipe with flexible hose at the top and it has a tee at the bottom with two short lengths of capped 25mm pipe fitted to the tee. I have drilled downward pointing (between 30 and 60 degrees) 10mm holes into the pipe and move it slowly like a vacuum cleaner. It works a treat. If you use a sediment trap, the sediment is like talcum powder.
On the other thread you mentioned that you were using schedule 40 (pressure) pipe. This pipe is very expensive here and I am sure that it would be similar in the US. You should check the price of DWV pipe. You can join sch 40 pvc and DWV pipe by using female fittings and poly nipples that are also available in reducing sizes. Upsizing DWV pipe is easy to do and the 100mm DWV pipe is cheaper here than the smaller sizes.
Suspended sediment settles as bed load and this builds up in wet system pipes. Your slope however means that a good proportion of the run will effectively be a dry system but the ground level pipe will nevertheless remain full of water to the level at the top of the vertical riser unless drained. I think that it would be worthwhile to install a sediment trap in this flooded section.
A sediment trap needs to be fitted in a non turbulent section of pipe but the water entering the flooded section in your system will be turbulent. The best distance downstream of the convergence between the dry and wet system to install a sediment trap is usually +5 metres but the distance depends on the pipe size and velocity as well as the pipe's remaining length. Unless the system flows at greater than 1 metre per second, installing the trap about 5 metres from the last area of turbulence is ok.
Bed load is either stationary or slow moving and when it reaches the trap, it simply falls down and is later flushed, minimising sediment in the tank(s).
The diagram below shows a 100mm DWV pipe wet system sediment trap made from off the shelf fittings.
If the water is for potable use, then the hose and pipes should also be suitable for contact with drinking water. It doesn't have to be high pressure hose/pipe because 1 metre (39 inches) of head is only 9.81 kPa or 1.42 psi. The volume or weight of water in the tank is incidental, the pressure only and not the weight relates to the hydraulic head pressure.
We use UV stabilised corrugated pond hose for balance lines when the tanks are reasonably close together because they are flexible. Tanks flex as they fill, see the second photo below.
An internal bell mouthed overflow is shown below. The bellmouth greatly increases the overflow capacity but if you are in a low intensity rain area, it is probably not necessary. Note that the overflow outlet is fitted lower down the tank because of the elbow and the bellmouth's rise.
Two overflows can also be joined to a single vertical overflow pipe, see below.
SUGGESTED DESIGN
Note that I have reversed the inflow and pump tank from your diagram.
All of the inflow diverts to tank 1 and decants through to tank 4. Unless it is a long duration heavy rain event or the tanks are reasonably full, the balance line from tank 3 to tank 4 is usually closed and cracked open several days later. The water that decants to tank 4 will be of very good quality.
Water diverted to a tank must pass through mosquito proof mesh here in Australia and this should apply to all countries.
A settling system provides natural filtration yet it is remarkable the number of multi tank installations that are plumbed with the pump drawing water from the infeed tank!
Rainwater is naturally acidic, it is a good idea to fill a nylon bag with limestone chips and place it in the tank to neutralise acidity. Tether a small buoy to the bag for easy retrieval.
Avoid using copper pipes when using harvested rainwater.
Only one overflow pipe is needed when all of the water is diverted to one tank but the tank's overflow capacity must be greater than the inflow capacity during a major storm event.
Don't have an overflow outlet fitted to the other tanks unless you block it off...remember that the water will rise above the bottom of the tank 1 overflow pipe in order to drain and if the tanks are full, this will cause water to flow from all overflow outlets. We have pvc caps here that fit neatly into the overflow outlet fitting and no doubt they would also be available in the US.
It is strongly preferable to let the water breathe and so the other three top meshed inlets should not be sealed but placing some shade cloth over the mesh will still allow air circulation while preventing sunlight ingress.
Using a tee at the base of the vertical riser allows you to divert an additional pipe away from the tank so that the wet system can be flushed. Being down hill at the lowest point, the additional pipe can also be a length that allows it to be used as a first flush diverter and the first flush manually drained to anywhere you like. First flush diverters with internal filters and a slow dripper are high maintenance and waste yield, having a larger manual drain valve is much better.
In reality, if leaf diverters and a sediment trap are used, the wet system shouldn't need flushing although the line could still be largely flushed through the sediment trap if there was an extended dry period. This then gives the option of fitting a flexible low restriction hose between the Tee fitting and an inlet valve fitted about 100mm above the bottom of the tank. This inlet will have priority flow because the tank's water level will always be lower than the usual height of the water at the top of the vertical riser, giving the inlet more head pressure that the vertical riser. We refer to this additional flow path as a low restriction inlet because the water doesn't have to flow up a vertical riser.
Advantages of having a low restriction inlet includes retaining less water in the wet system, the wet system will be flushed every rain event, the wet system will only retain the last (cleanest) water diverted during the rain event, the oxygen rich water will oxygenate the tank 1 anaerobic zone which improves the water quality PLUS the additional inlet increases the maximum flow rate through the wet system, allowing the use of smaller pipes or compensating for an inadequate hydraulic head.
It should be noted that standard rainwater harvesting systems deliver water to the top of the tank and draw water from the anaerobic zone at the bottom of the tank, the opposite to what is best! To draw water from the cleaner upper levels, you simply install a floating outlet hose to the outlet valve that supplies the pump...see link below.
http://www.crystalclearwater.com.au/waterboy/
A floating outlet hose with an attached fine filter.
We have what we call downpipe wall spacers and these or similar can be used to stabilise the inflow pipe above the tank's top meshed inlet. The photo below shows this fitting as well as a flap valve fitted to the end of the pipe. The flap valve prevents mosquitoes and birds etc from entering the pipe.
The horizontal pipe at the top of the vertical riser must be checked for a downward slope before being secured.
The balance valves between tanks 1 and 2 should be about 100mm above the bottom of the tank at the valves lowest points but the other balance valves can be 60-70mm above the bottom of the tank.
If the tanks are desludged, it is best to remove the tank's top meshed inlet and use a siphon or similar. This is best done when the tanks water levels are high. I have a syphon that I made from 25mm (1") pressure (sch 40) pipe with flexible hose at the top and it has a tee at the bottom with two short lengths of capped 25mm pipe fitted to the tee. I have drilled downward pointing (between 30 and 60 degrees) 10mm holes into the pipe and move it slowly like a vacuum cleaner. It works a treat. If you use a sediment trap, the sediment is like talcum powder.
On the other thread you mentioned that you were using schedule 40 (pressure) pipe. This pipe is very expensive here and I am sure that it would be similar in the US. You should check the price of DWV pipe. You can join sch 40 pvc and DWV pipe by using female fittings and poly nipples that are also available in reducing sizes. Upsizing DWV pipe is easy to do and the 100mm DWV pipe is cheaper here than the smaller sizes.
Suspended sediment settles as bed load and this builds up in wet system pipes. Your slope however means that a good proportion of the run will effectively be a dry system but the ground level pipe will nevertheless remain full of water to the level at the top of the vertical riser unless drained. I think that it would be worthwhile to install a sediment trap in this flooded section.
A sediment trap needs to be fitted in a non turbulent section of pipe but the water entering the flooded section in your system will be turbulent. The best distance downstream of the convergence between the dry and wet system to install a sediment trap is usually +5 metres but the distance depends on the pipe size and velocity as well as the pipe's remaining length. Unless the system flows at greater than 1 metre per second, installing the trap about 5 metres from the last area of turbulence is ok.
Bed load is either stationary or slow moving and when it reaches the trap, it simply falls down and is later flushed, minimising sediment in the tank(s).
The diagram below shows a 100mm DWV pipe wet system sediment trap made from off the shelf fittings.
SaveH20 - you and your bro (Diver) are the man!!!
I've read through your post,(btw - awesome as usual) and will be incorporating many of the ideas you suggested. I will be working on getting the system ready over the next few weeks, but it appears the rains have started early this year so I may get the tanks filled before I have the pump house and pump hooked up. I will have to wait for a break in the weather to get that setup.
I'm thinking about using a Grundfos CMBE pump as my pump. It's a pressure tank, pressure switch and pump all wrapped up into one unit. I spent some time talking to Grundfos tech today and they said it's a real work hog of a pump. (http://us.grundfos.com/products/find-pr ... oster.html)
I will take pictures and update it here as I go along.
My only concern / regret is that I used a 75mm pipe to route the water to the tanks instead of a 100mm pipe. I followed the advice of a couple of guys here who work for ag. pump companies and kick myself for not following my own gut feeling that the pipe might be too small. Unfortunately, the pipe is buried and the ground is a mud pit now due to all the rain we're getting so I will just have to live with it for this season.
I can't thank you guys enough for all the help and advice.
Have a great day!
Dennis
I've read through your post,(btw - awesome as usual) and will be incorporating many of the ideas you suggested. I will be working on getting the system ready over the next few weeks, but it appears the rains have started early this year so I may get the tanks filled before I have the pump house and pump hooked up. I will have to wait for a break in the weather to get that setup.
I'm thinking about using a Grundfos CMBE pump as my pump. It's a pressure tank, pressure switch and pump all wrapped up into one unit. I spent some time talking to Grundfos tech today and they said it's a real work hog of a pump. (http://us.grundfos.com/products/find-pr ... oster.html)
I will take pictures and update it here as I go along.
My only concern / regret is that I used a 75mm pipe to route the water to the tanks instead of a 100mm pipe. I followed the advice of a couple of guys here who work for ag. pump companies and kick myself for not following my own gut feeling that the pipe might be too small. Unfortunately, the pipe is buried and the ground is a mud pit now due to all the rain we're getting so I will just have to live with it for this season.
I can't thank you guys enough for all the help and advice.
Have a great day!
Dennis
I appreciate your appreciation!
I was wondering whether you had plumbed the pipe the full distance. Did the 'experts' also advise you to use the sch 40 pipe? Those guys should know what your area's 1:10 5 minute intensity is...why not ask them? Surely they based their recommendations for the pipe size on those figures.
If you can find out what the 5 minute intensity is for your area's 10 year return event, you can compare the 1:10 roof harvest rate Vs the wet system's maximum flow rate to see whether there would be a problem during a heavy rain event. Your pipe with (my guesstimated) 150 meters of friction loss and a 3 metre head will give a little less than 350 litres per minute which equates to rainfall that is a tad less than 2 mm per minute.
Tt requires 4 times the head to double the flow rate and while flow rates at lower heads are impressive, there are big increases needed to make up any requirement discrepancies. You can play around with the 2 flow rate calculators below to see for yourself what the variances are. The uPVC roughness coefficient is 150 and other measures can be changed.
http://www.calctool.org/CALC/eng/civil/hazen-williams_g
http://www.nationalpump.com.au/calculat ... alculator/
Have you already experienced double omega blocks and if so, did they bring greater rain or just cause cold weather? There were times earlier this year when it was hotter in Siberia than it was in California and large parts of the central US flooded. The North Polar Jet Stream is a mere semblance of its former self and the consequent changing weather patterns must also be factored as historical records are now truly history so to speak.
https://www.youtube.com/watch?v=GtC_Qf1Zd4Q
I am a big fan of Grundfos pumps and having variable speed drive is ideal for household use. You will need a larger than usual internal diameter hose to pump water 122 metres without a lot of friction loss and don't forget to fit a check valve. You can use the second flow calculator I linked to see the friction losses with different internal diameter hoses and flow rates over the distance.
My only concern / regret is that I used a 75mm pipe to route the water to the tanks instead of a 100mm pipe. I followed the advice of a couple of guys here who work for ag. pump companies and kick myself for not following my own gut feeling that the pipe might be too small. Unfortunately, the pipe is buried and the ground is a mud pit now due to all the rain we're getting so I will just have to live with it for this season.
I was wondering whether you had plumbed the pipe the full distance. Did the 'experts' also advise you to use the sch 40 pipe? Those guys should know what your area's 1:10 5 minute intensity is...why not ask them? Surely they based their recommendations for the pipe size on those figures.
If you can find out what the 5 minute intensity is for your area's 10 year return event, you can compare the 1:10 roof harvest rate Vs the wet system's maximum flow rate to see whether there would be a problem during a heavy rain event. Your pipe with (my guesstimated) 150 meters of friction loss and a 3 metre head will give a little less than 350 litres per minute which equates to rainfall that is a tad less than 2 mm per minute.
Tt requires 4 times the head to double the flow rate and while flow rates at lower heads are impressive, there are big increases needed to make up any requirement discrepancies. You can play around with the 2 flow rate calculators below to see for yourself what the variances are. The uPVC roughness coefficient is 150 and other measures can be changed.
http://www.calctool.org/CALC/eng/civil/hazen-williams_g
http://www.nationalpump.com.au/calculat ... alculator/
Have you already experienced double omega blocks and if so, did they bring greater rain or just cause cold weather? There were times earlier this year when it was hotter in Siberia than it was in California and large parts of the central US flooded. The North Polar Jet Stream is a mere semblance of its former self and the consequent changing weather patterns must also be factored as historical records are now truly history so to speak.
I'm thinking about using a Grundfos CMBE pump as my pump. It's a pressure tank, pressure switch and pump all wrapped up into one unit. I spent some time talking to Grundfos tech today and they said it's a real work hog of a pump. (http://us.grundfos.com/products/find-pr ... oster.html)
https://www.youtube.com/watch?v=GtC_Qf1Zd4Q
I am a big fan of Grundfos pumps and having variable speed drive is ideal for household use. You will need a larger than usual internal diameter hose to pump water 122 metres without a lot of friction loss and don't forget to fit a check valve. You can use the second flow calculator I linked to see the friction losses with different internal diameter hoses and flow rates over the distance.
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