Improving existing rural water catchment and storage system

Good morning,
We recently moved into a 20 year old bush block in Tasmania. When it was built, all stages of construction got the council stamp of approval but when looking at some elements of the build, I can’t imagine how!?
The block is connected to the electricity grid but is solely on tank water and septic waste. The water catchment and storage system requires much improvement, especially improving the quality of our standing water in the charged pipes.
I’ve spent many hours scouring previous posts and have learnt a massive amount (thank you to all previous contributors) but haven’t found exactly what I need to know and would love some feedback/suggestions.

Current situation

The 1:20 ARI for the region is =122.4mm/hr.
The roof is colorbond and gutters are colorbond but all with different profiles and some not with the correct fall. The roof has 11 degree pitch and has a verandah to the North of Section A and carport to the south of section C.
The horizontal area of the roof sections are (m2);
A= 60
B= 40
C= 72
D= 46
With a total of 217m2 (excluding gutters).

Water tanks 1-5 are fibreglass, tank 6 is poly. Tank 6 is reserved for Firefighting but only legally require 10kL of stored water. We are in a high fire risk area, so want this tank to remain full.

Tank sizes are
1= 25kL
2,3,4,5= 15kL
6= 24kL
With a total of 109kL
Tanks 1-3 are about 5-7m above the house.
The top of Tanks 4 and 5 are about 2-3m below our gutter
Tank 6 is about 40cm below tanks 4 and 5.

With the exception of some downpipes (50x100mm), all other PVC (RED line in diagram) is 90mm stormwater, including the charged pipes…)
All other water fittings (BLUE lines in diagram) are 25mm rural polyethylene pipe (green stripe)

When we moved in, chicken wire was sitting in the gutters over the downpipes, there was 400mm access/inlet hatches on each of the 6 water tanks. They had previously had fibreglass flyscreen but have all disintegrated.

Tank 6 is filled by the overflow of tanks 4 and 5.
Tank 4 is filled from rainfall. 4 and 5 are balanced.
A pump located on balanced line (of tanks 4 and 5) pumps up the hill with a pressure switch and float valve on tank 3.




Tank 1,2 and 3 can all be balanced but I tend to isolate either tank 1 or 2 as a redundancy incase of catastrophic system failure.
Our house water is gravity fed from a mixture of either (tank 2 and 3) or (tank 1 and 3).

So far, our water is clear and doesn’t smell or taste foul BUT I know that there is significant sediment in all tanks (especially tank 4).




To start with;
- I have placed a leaf beater on each of the downpipes (sorry, can't figure out how to rotate photos). Due to the significant head height, the leaf beaters are located below eye level so they can be seen easily and regularly maintained.
-I have placed stainless steel mesh on all inlets and outlets (including tank overflows, which I now know isn’t a great idea for maximising outflow)

Future plans
I would like to;
-replace gutters and ensure they have the correct fall.
-upgrade all PVC plumbing to 100mm (mostly for increased strength)
-upgrade my leaf beater system to address the flaws with this particular model
-combine the downpipes of roof sections C and D together and A and B together. -combine all catchment pipes to one section of PVC between the house and tank 4
-install a sediment trap (same style as SaveH20 has documented)
-install low restriction inlet at the bottom of tank 4, with supplemental 100mm riser
-have option to dump all standing water in cases of drought (ie isolation ball valve as part of low restriction inlet)
-use tank 4 as a settling tank
-use tank 5 as potable water to be pumped up to header tanks 1,2,3
-keep using tank 6 as fire fighting tank and emergency drinking water
-have floating outlet (maybe with check valve but maybe not necessary?) going from tank 4 into bottom of tank 5.
-Have floating outlet in tank 5, being pumped up to header tanks 1,2 and 3.
-Have overflow from tank 4 to have tank vac (or something similar into tank 6
-Overflow from tank 6 to go into draining trench, drawing overflow from the diameter of the base of the tank (with slots)
-I don’t plan to have any formal first flush diverters. I’m hoping that the sediment trap and low restriction inlet (combined with settling tank) should function well enough.

Questions

Will a tank vac still work if its flow is redirected to tank 6?
Is a check valve between tank 4 and 5 necessary?
Does this all seem like a reasonable plan?
Does anything seem redundant or ridiculous?

Very happy to hear your opinion or any suggestions for improvement and can elaborate on my plans if further clarity is needed.

Cheers

Excellent information, it certainly makes answering the Qs very easy.

Your system is actually well set up as far as standard wet systems go and certainly a lot better than most of the rural systems I get to see or asked to troubleshoot. However, there is room for improvement to attain rainwater harvesting best practice.

Having an adequate wet system sediment flushing velocity even if only at times during occasional heavy rain is essential to deliver good quality water as unflushed pipes build up sludge and promote anaerobic conditions.

(ND) 90mm pvc stormwater pipe has an internal diameter of 86.2mm which = a capacity of 5.8 L/metre. A velocity of 1 mps = 348 lpm (34.8 lpm @ 0.1 mps). Currently, one 90mm stormwater pipe harvests a 72 sq m roof (C) while the other pipe harvests a total of 145 sq m from rooves A, B and D. The pipe harvesting the three downpipes will have a chance of occasionally achieving a feasible flushing velocity but not so the pipe harvesting 72 sq m.

A major wet system design flaw I noticed while researching wet systems pre Supadiverta is the use of a same size pipe all along the wet system which means that one and commonly more downpipes furthest away from the tank provide no flushing velocity. This can have serious long term ramifications. Even with the smaller 90mm (86.2mm ID) stormwater pipe used in your system, the downpipe harvesting Roof B (40 sq m) would only collect a tad more than 80 lpm during heavy rain that reached 1:20 Average Recurrence Interval (ARI) status. With a flow rate of 34.8 lpm @ 0.1 mps, 80 lpm is only 0,23 metres per second.

If you were to use a 100mm DWV pipe which has an ID of 104mm and a capacity of 8.5 L/m, a V of 1 mps = 510 lpm or 51 lpm with a velocity of 0.1 mps.

It has to be remembered is that a pipe diverted to a water tank is NOT a stormwater pipe and not applicable to those regulations, in fact, the regulations do not permit stormwater to be collected for rainwater storage. If the tank's overflow pipe connects to a Legal Point Of Discharge (LPOD), the pipework is covered by stormwater legislation.

Because you have fitted leaf diverters, a good size pipe you can use between the roof B dp and roof A dp would be a 50mm DWV pipe. You have a lot of head and the 50mm DWV pipe has an ID of 51.6 mm and a volume of 2.01 L/m.

Because tank 4 accepts the diverted water from vertical risers that discharge above the tank, the wet system pipes remain full to the level of water retained at the top of the risers when it stops raining unless you fit a low restriction inlet valve. You are able to do this because you have fitted mozzie proof leaf diverters to all downpipes.

Re providing water to the house from either tanks 2 + 3 or 1 + 3, just remember that you are halving the velocity through each branch line.

Upgrading to 100mm DWV makes fitting a DIY sediment trap a breeze. The pipe reducer shown in the diagram has now been replaced by an invert taper. You lose minimal water when occasionally flushing the captured bed load, the capture is continuous and the retained wet system water is the last water off the roof which is the cleanest.

Can you drill a hole in a fiberglass tank? Having a low restriction inlet will retain a lot less water in the wet system between rain events because the water in the riser and the pipes will never be higher than the water level in the tank.

You should always use a flexible UV stabilised hose and a ball valve. I recommend using a poly nut and tail to connect the hose to a poly nipple (a poly nipple has a male thread at both ends). The poly M+F elbow in the photo is also angled and the hose is 50mm.

Using tank 4 as a settling tank is ideal. Also having floating filter intakes in tank 4 and tank 5 is an excellent idea as you will be drawing the best quality oxygen rich water in the tank. Our new floating filter intake is undergoing final prototyping and will be superior (and cheaper!) to current versions currently sold.

You can make a simple portable syphon/vacuum to clean the bottom of the tanks. I made one with a length of pvc pipe fitted with a pvc pressure valve socket connected to a faucet (female threaded branch) tee. The tee has a short capped.pvc pipe at each end and there are some holes drilled in the tee and slots about 5mm wide cut into the pipes. Slots are more efficient than holes and they are placed at about 135 degrees downwards. The total open areas are about x 2.5 the standing pipe's open area. A poly pipe connects to a faucet tee (pressure fitting at the top as it is easier to prime the suction if you fit an inline valve within arms reach part way down the standing pipe and a plug to the tee's port which needs to be also fitted with a short pvc pipe and a pvc pressure faucet socket. To prime, close the inline valve, remove the air via the tee, open the inline valve and vacuum the tank's floor.

Once you vacuum the tanks, it will take a long time for sludge to accumulate again when using a sediment trap...actually, the sludge won't be sludge, it will be a minimal spread that is much different (finer) to normal sludge.

Questions

Will a tank vac still work if its flow is redirected to tank 6?
The TankVac uses a 800mm long vertical syphonic downpipe section that generates syphonic flow. In short...no. The sketch shows water flowing up hill.

Is a check valve between tank 4 and 5 necessary?
It would have to be spring loaded to work and that would be an issue with gravity flow. Just manually open a ball valve whenever necessary.

Does this all seem like a reasonable plan?
Yes. Well thought out and a good example of rainwater harvesting best practice.

Does anything seem redundant or ridiculous?

It is best practice to have a flap valve on a vertical riser's discharge port.

Do you have copper pipes? Rainwater is naturally acidic but putting some limestones in tanks 4 and 5 would remedy this.

Last diagram, tank 6. You would need a hole at the apex to safeguard against a continuous syphon if one was to form...which would be near impossible. To create a tank's bottom suction effect, you would need the bottom horizontal pipe to be connected to a low outlet and manually open the discharge during times of excess. It won't work as per the sketch.

Thanks for your response SaveH20. I was hoping for some good feedback and you've brought it. I'd appreciate a bit of clarity with a few things you've mentioned though.

Am I right in thinking that the sediment flushing velocity needs to be adequate (> 0.5 metres/sec) to flush all horizontal sections of pipe (ie between each down pipe and from downpipe D to water tanks.) And that pipe diameters need to be considered to make sure the appropriate flushing velocity is achieved during 1:20 ARI events. The larger the diameter of the pipe, the slower the velocity of water passing through it, which means it might not be fast enough to clear accumulating sediment?

I'll do some calculations for the downpipes and horizontal pipes and come up with a plan for pipe sizes/joins and post them soon.


Is there an ideal length for the 40mm DWV length? I can imagine too long and you waste too much water but too short and the sediment can become disturbed. I have a lot of flexibility with this but can't really figure out the best length/location for it.

Yes. I have drilled through the top wall of my fibreglass tanks (and collected the fibreglass dust/shards before they entered my tank), to install the inlet polynut and tail. Not sure if it is possible to drill down near the bottom and still maintain a watertight seal, i'll have to find out.

The photo that you have of your low restriction inlet, Do you always use 50mm and do you use the 90 degree elbow to help minimise stress on the poly nut and tail? What is the purpose of the flexible pipe? I was just expecting to just have a 100mm PVC Tee on the riser with a 50mm invert taper going straight into the tank. I remember seeing something about this on other posts but couldn't find it again...


I had trouble visualising your portable syphon system, do you have any photos? It sounds like I made something similar a few weeks ago which connected to 25mm green stripe poly pipe which had good suction but was too hard to use effectively due to the flexibility of the PVC pipe and stiff/heavy 25mm poly pipe. I've attached a photo of what I made and the filth being extracted from tank 1. I'd like to refine this system.








Is there any way to put this expelled water to use? I'm imagining that once my tanks are clean and my leaf diverters, and sediment trap are operational, I shouldn't have much sediment building up. As it will be my settling tank, it would be nice to find a way to remove that sediment automatically BUT also find a use for the mostly clean water.


Is this so when water flow is real fast, the mesh opens and doesn't slow things down?


Only have copper pipes around the hot water tank. I'll look into increasing the pH with lime. Thanks

If I don't use a check valve and don't use a manual ball valve, will I run into any strife?
-When the settling tank is higher than the potable tank, water should transfer from tank 4-5.
-When the tanks are even, no transfer should occur
-I can't imagine a scenario when the potable tank will be higher than the settling tank.





The hole at the apex is a great idea if I was expecting it to syphon. I initially thought I wanted to make a low-tech version of the tankvac but don't really need the velocity and volume of the vacuum suction effect.
Just a regular overflow BUT instead of taking water from the top, it took it from the bottom (with most sediment and deoxygenated water). Similar to the product available from Blue Mountain but with the benefit of drawing the water across the diameter of the tank (and not just one location). Will my previous sketch function as a simple overflow?

If not, how about the overflow as pictured on the diagram below?

If I am certain that I want a tankvac on tank 4 and can't direct the outflow into tank 6, then tank 6 will never be filled and it won't need any outlets!

If the tankvac system is useless at filling other tanks, then perhaps I save some money, ditch tankvac on tank 4 and make a low-tech overflow system (like I had planned for tank 6 ) and have that direct the overflow from tank 4 to tank 6 through a calming inlet similar to the diagram below?




Thanks again for your feedback, it is nice to see this project come closer to fruition!

Correct!

This is undoubtably the most important but also the most overlooked, unconsidered or just plain unknown facet of rainwater harvesting wet system design. Wet systems have a bad reputation but l'll go into a bit of detail here because a lot of people who read these threads have wet systems and it is vital to have an understanding of laminar Vs turbulent flow and their respective affects on sediment transportation and how they can be used to advantage

LAMINAR FLOW:
Water flows in boundary layers aka streamlines due to the friction of the pipe's walls resisting the flow. This phenonema causes water to flow fastest through the core and slowest against the pipe's wall. In many instances, the water on a pipe's wall regardless of whether it is at the top, bottom or side will be stationary. Laminar flow boundary layers do not mix!

Negligible particulate transportation but great area to fit a sediment trap.

TURBULENT FLOW:
Turbulence is caused either by a flow disruption or favourable velocity and is chaotic due to there being vortices, eddies and the mixing of boundary layers. Detritus is either suspended or pushed along the pipe unless the flow becomes laminar.

It is an endemic mistaken belief that sediments are transported by all moving waters and accumulate near the vertical riser. When there is laminar flow and insufficient velocity to maintain sediment suspension, the resultant bed load reconstitutes as a few small 'colonies' but once their size becomes high enough to be agitated by the increasingly faster boundary layers above, a small section will break away at the front and quickly travel along the bottom of the pipe to the next colony where the action is repeated. It is like watching a fascinating relay race. In time, the colonies increase in numbers and get bigger until there is one long colony that continues to build.

When organic matter is in the bed load, anaerobic loving bacteria will break down their nutrient feast which decreases the oxygen level. Bacterial die off then becomes part of the sludge which often forms a black tarry resinous substance that sticks to the pipes and is often seen in water tanks.

Large pipes at the head of a wet system are really bad news because the velocity even during heavy rain events is insufficient to generate or maintain an adequate flushing flow rate unless large roof areas in high intensity rain areas are harvested.

The video below unfortunately doesn't explain why increased velocity transitions laminar flow to turbulent plus most of the objects selected also project into the small pipe's higher boundary layers. I would have liked the vertical riser to be extended as a separate demo to show the effect of reinstated laminal flow on the suspended items but it is still worth watching. As you will also see, the disrupted flow through the elbow generates a lot of turbulence.

https://www.youtube.com/watch?v=c1xX90ZfBj4&t=347s

It doesn't have to be 40mm, it just has to generate enough velocity (turbulence) to flush the captured bed load. When flushing, you will see initial clear water then a slug of dirty water. That is when you close the valve. Incorporating the trap into the wet system will result in beter quality water and significantly lower yield loss due to the increased flushing efficiency.

The inlet's size depends on the carrier pipe size but when two pipes merge at a tee, then the tee is upsized and bushes fitted to the other two sockets.

The 90 degree threaded M+F poly elbow connects to the flexible pipe from any direction including from underground. It should be fitted within 75 degrees of the outlet that supplies the pump but not too close because of turbulence unless you are using a best practice floating filter.

You should never use a hard fitting on a tank or pump. The photo below shows what happened to a balance line due to tank distortion as it filled. If it was a pvc pipe, all water would have been lost.


Yes, that's it but make it smaller.so you can manage it better. I have a 32mm one and the two visible pressure pipes between the tee and the caps are only exposed 100mm each but size and length depends on the tank's floor area. It is interesting that you used slots, they are much more efficient than holes. Also drill a hole near the bottom of each cap to extend the suction range.

When you have the sediment trap fitted, you will have minimal need to vacuum the tank for many years. The link is to one member's post commenting on his sediment trap. viewtopic.php?p=1551215#p1551215

Fitting a flap valve to the vertical riser discharge port prevents mosquitos and other pests having access.


Are there not ball valves already fitted?

The TankVac initiates the syphon in the 80mm diameter 800mm long external overflow pipe. To do it, you need 'plug' flow to purge the pipe of air and the mechanism needed to do this is fitted inside the external pipe. It isn't rocket science to make but if you use a sediment trap, you will have minimal sediment and a much different type of sediment anyway.

The Blue Mountain 'vacuum' depends on having sufficient velocity up the pipe to transfer sediments and the velocity/flow rate will always be the same as the inflow rate. It is NOT a syphon in itself. The serated bottom edge has a minor cleansing affect in the immediate area but that's all.

Re Tank 4-6, why not retain the status quo

Thank you for your response, that has cleared most things up for me.
I've had a bit on my plate recently so have had to put the water catchment project on hold for a bit but will be in touch (with some photos) once I get things up and running. I'll shout out if I need any further advice.

Looking forward to seeing your finalised floating outlet device!

Cheers

The floating intake filter is on temporary hold because I am about to prototype and test some late changes that I obviously can't detail here. This has delayed the 3D printing of two parts.

I am also negotiating to have a small inflatable buoy manufactured for customers with non potable use to reduce the packaging/post costs. The ones I have found so far are too big and often the wrong shape. Rigid ball floats suitable for use with potable water will also be available.

Our floating intake filter will be a vast improvement and also cheaper than ones currently sold.