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NickM

Rainwater Harvesting: using copper pipes

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HI All,

I'm not sure if this is the right place to ask, but I've read some really useful forum threads here about rainwater harvesting, so here's my question:

I've got a rainwater harvesting tank and small pressure-controlled pump which is currently totally independent from my municipal supply. However I'd like to put a couple of toilets and washing machine onto rainwater, but obviously can't guarantee a year-round supply. I should be able to isolate those 3 supply points onto one line such that they can be fed by rainwater, and then switched over to municipal if I don't have any rainwater in the tank. The switch would just be at one location - I don't want to have to drill new holes into the water at all 3 places and have some kind of switch (eg: below the toilet) to manually switch over each one - that would be madness. 

What this means though, is that these fittings (2 toilets and washing machine) would be supplied via their existing copper piping downstream of the "switch over" point. I've heard a few people say that you should not use copper pipe with rainwater as it tends to be acidic and may corrode the pipe. I'll wont be drinking this water, but I don't want to have to replace the pipes after a couple of years. Does anybody have any experience with this/know much more about it? Is just a bad idea if you plan to drink the water, or will the acidity of the rainwater destroy the pipes pretty quickly?

Thanks in advance

Nick

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Hi NickM,

I am not an expert, but I did my rainwater setup 3 years ago - first connecting the toilets and washing machine, then connecting the entire house once the water restrictions kicked in in Cape Town. I did some research at the time.

  • Rainwater can indeed be quite acidic. I measured the pH a few times and it varied from 5.5 to 7.0. So if your copper pipes are long, or difficult to access, you are probably exposing yourself to some annoying leaks after a few years. My best experience is with Cobra pipe. My worst is with PVC pipes (leaks around the glued fittings if the pipes move a bit).
  • In the setup you describe, I am a bit worried that you are using connected piping for potable water and non-potable water. Rainwater is not "clean": the moment you store it in a tank, you will have germs, algae and bloodworms. Running that water through the pipes that are also connected to your potable water at other times of the year could be problematic, from a health point of view and from a regulatory one. In my case, I did a parallel setup with a switch by each toilet (what you described as "that would be madness" 😉) - but I have enough water to never have to use those switches.

Hope this helps!

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Posted (edited)

Thanks Oli4,

If I were to go the route I described, there would be a part of my domestic pipe network (2 toilets and a washing machine) that could be supplied by either rainwater or municipal - but it would be entirely isolated from the rest of the network via non return valves. So there would be no chance of rainwater ever making its way into drinking water, unless I decided to drink water out of the cistern. So far it's just my dog that likes to do that (OK technically the bowl). Basically the last few meters of the supply to 2 toilets and a washing machine would use the existing copper pipe, in an effort to avoid having an entirely parallel system. It would just be less work and be much neater... if it is possible. 

Good to know about the PVC and Cobra pipes. I've actually connected the pump up with PVC, but I'm still not supplying anything inside yet. So far so good. 

Cheers

Nick

Edited by NickM

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I'm not sure if the following is legal in terms of keeping municipal and rainwater/greywater separate but it's something I'd do without it bothering my conscience.

If you want to make the change over system automatic you could install a ball float valve (like the ones in your toilet cistern) inside and close to the bottom of your rainwater tank and connect it to the municipal supply. When the rain water level in the tank drops to say the 25% capacity the ball float valve will open and maintain the level at 25% using municipal water. Just determine where the crossover point needs to be by moving the ball float valve up or down inside the tank.

Your booster pump will never run dry unless there is no rain water and the municipal supply is off and you'll never need to worry about manual intervention. Alternatively install a float switch in the tank so that the booster pump can't run when the tank is below a certain level.

The ball float valve prevents rain water from feeding back into the municipal supply although the municipal pressure will almost always be higher than the head of water in the tank (except when there are water outages or if the tank is on a very high tank stand in which case you wouldn't need a booster pump). Regardless it's not possible to accidentally feed rainwater back into the municipal supply using a decent float ball valve.

N.B. Just make sure that the outlet from the ball float valve is in clear air (not underwater) when the valve starts to open. This prevents siphoning/feedback into the municipal supply when the municipal supply is off and the level in your tank is in the "top up" area. You can do this by bending the float arm downwards or installing the valve at a tilted angle so the float is lower down than usual.

Edited by Surge

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Hello guys,

I am also interested in using some of my rainwater for the toilets, dishwasher and washing machine.

My question to @Surge is whether you filter and drink the water from your rainwater system. How do you treat that water before it is drinkable?

Thanks for the information.

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2 hours ago, Goedman said:

Hello guys,

I am also interested in using some of my rainwater for the toilets, dishwasher and washing machine.

My question to @Surge is whether you filter and drink the water from your rainwater system. How do you treat that water before it is drinkable?

Thanks for the information.

I am not Surge, but I do filter and drink my rainwater. 

I would always recommend you first have your water tested for biological and chemical content (Bemlab does it).

If you are located in an area where your roof may gather pollutants, you will need a reverse osmosis system. Pollutants may come from being located near fields where pesticides are used, busy roads, factories, an airport, etc. Reverse Osmosis is the only effective way to get rid of metals and chemical compounds.

If you can assume your roof is not gathering any pollutants other than organic stuff (leaves, bird poop, dead geckos etc), you can use a more simple system with "big blue" filters (5-micron sediment filter, carbon filter, 1-micron sediment filter) followed by an ultraviolet (UV) purifier. This system is interesting because it is very cost effective, and can easily process a flow of water sufficient for the entire house. An RO system cannot do that: you will need to have a holding tank after your RO system, to keep your filtered water. I would recommend you still put a UV purifier after your holding tank, before the water is supplied into your house.

Some local regulations will force you to have an "air gap" to separate municipal water and your own water, to prevent polluting the municipal reticulation system.

I hope this helps.

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hi @NickM and others here - rainwater harvesting, interesting topic and, like all others out there, often misused and abused to further certain agendas. i've been doing it for ten years, our grandparents and whoever before them had to do it over the millennia, so to make it complicated is way over the top if it is intended for personal and small scale use.

yes, rainwater is acidic - but how long will this take to corrode your copper pipes? in other words would it be cost effective to replace your piping? i do not know, neither do i know if you will die from it; but rest assured, die you will from something 🤣

is static rainwater in your tank going to go bad?... yes, if you do not do something like treat it with ordinary household bleach or something containing sodium hypochlorite or another method, see below.

we have one 5000l tank getting water from a section of roof and just a roll of chicken-wire mesh to keep out the worst as filter. it has NEVER been cleaned out BUT it has a simple electrolytic sanitizer and after 10 years the water is free of bacteria, organisms and slime and looks pristine, does not smell and above all tastes great. i myself and many others regularly use the water for drinking purposes ... no ill effects yet 😉

before we get to the simple mechanism please note that copper, by virtue of its oxidation, has a 'natural' antibacterial effect; for instance modern steel and aluminum door handles are far worse than the old copper used for handles when it comes to harboring bacteria etc.

ok, the 'gadget' is a solar-powered anode and cathode , one piece silver [small, cent size will last about 100,000 years plus] and copper as in pic - voila, image attached

the who instructions for sanitizing water [attached]  are somewhere on their web site but it boils down to 250ml jik per 5000l water in reasonable condition, i.e. if the water comes from your roof into your tank a cup of jik per 5000l every month [obviously this will be influenced by the rate you use it] should be more than sufficient to keep it potable.

a very interesting site is here https://www.lenntech.com/

God bless

g

waterioniseerder.jpg

who chloride.pdf

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@TRE30 hi! you can rummage through old family hand me downs, some cutlery etc was made from high grade sterling silver, alternatively try some jewelers or suppliers to the jewelry trade. remember a small piece will go a loooong way - it's a matter of quality not size!

let the forum know of the result of your 'hunt' 🙂

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I stay in Kenton on Sea, have had a house since late 70's

Here the principle has always been municipal water to toilets rainwater for everything else.

The water reticulation of the house has toilets supply separate from the rest ... bath, washing machine etc

I filter only my drinking water using 3 x big blues (Inline Cartridge Filters)  and a Doulton Rio 2000 multi candle filter  there are some people that use nothing and others that buy drinking water

For the rest bathing hand wash etc direct from the tanks

It seems you can make a rainwater system as complicated as you wish but I prefer the kiss rule

I have recently switched to a DAB AQUAJET 82 M Self-Priming Booster Pump With Pressure Tank

 

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