Revisiting rainwater harvesting in Singapore

Hi there,

 

I came across your blog when I was doing some research on rainwater harvesting systems (we are in the process of renovating an old inter-terrace house that that we just bought, and thought that this might be worth exploring).

 

I know that this is a question that you fielded a number of years ago (hopefully things have changed since then, as your answer then was that there wasn't much demand for this), but would you know what is available in the market in Singapore in terms of rainwater harvesting systems for domestic households (we are looking for a fairly straightforward above-ground system) and are there any that you recommend? 

 

Thank you,

 

Felix

Dear Felix,

Indeed, the rainwater harvesting (RWH) market appears to have developed in the past few years. I believe RWH is becoming more widely known and accepted in SG. That comes with a rise in demand for RWH and naturally, businesses will be built around servicing this demand.

I am actually happy to see this happening as it shows that people are becoming green not just in words but in action too. However, we also have to bear in mind that the current RWH solutions in the market are more geared towards a private house rather than a HDB flat. (On the other hand, RWH can be done at community level by e.g. HDB at Treelodge@Punggol in which the whole HDB estate is designed and built for RWH.)

Over the past years, I have come into contact with some of these businesses. A quick online search should yield the same results.

1. Green Eco Harvesting
   A quick glance shows that it is offering tanks and filters for RWH
2. Netatech
   It advertises construction of RWH system.
3. Hydro
   It features tanks and filters for RWH.

As for your question, no, I have no preference for the above or any other vendors. But if you decide to go ahead to integrate a RWH system into your house, a few points to keep in mind...

1. Does the vendor only sell you the tank & filter or does it include installation into your existing house structure?
2. What kind of maintenance is needed for your RWH system? Does the vendor offer such a service or are you on your own after its installation? Obviously, the cost and frequency of maintenance should be taken in consideration when you make your decision to get a RWH system.
3. Is your setup legal??? Legally speaking, the plans for your RWH setup have to be approved by PUB and NEA (if gutters are involved in RW collection). These plans are typically submitted by a QP/PE/architect to the authorities. Is the vendor doing these for you or are you expected to engage your own QP/PE/architect to do so? Finally, legal means additional costs so factor that in too!

Good luck!

Figure: using a zinc roof to collect rainwater (Water for Life, Hesperian Foundation)
Who says RWH has to be complicated? It has been and still is done simply and cheaply in developing countries. Mosquito breeding is a concern but not insurmountable with care and effort.

More questions on silver in water filters: Is it really safe?

Dear Chen Ko

 

Thank you for your reply and I just saw your timely blog post - thank you so much! And it is so comprehensive and helpful, as always.

 

I must say the facts on silver were not terribly assuring. I have a few quick follow up questions if you could help:

 

1. I saw the info below from http://www.arkwater.com/FAQ.html. They mentioned that the silver content is 0.07%, but I don't know how that number sits with the 0.1ppm (parts per million) you mentioned. Pls advise?

Why do the ceramic elements contain silver?  Are they safe?

In a multilayer candle, the protective effect is even more critical because carbon is a natural growth medium for bacteria.  In carbon-only filter elements, which are commonly found, the carbon filter often ends up as being a bacteria repositary if not changed regularly.
The silver in the Doulton® ceramic elements is a specially formulated self-sterilizing (bacteriostatic) agent.  The result is that bacterial growth is prevented from occurring within the Sterasyl® ceramic element (which is possible with the other ceramic filter elements).  More importantly, bacterial "grow-through" is eliminated.  The silver content is about 0.07%, which is well within the allowable levels recommended by the World Health Organization and the EPA.  Because of the silver, Sterasyl® filter elements do not require sterilization after cleaning.  Oligodynamic silver in Sterasyl® is permanently locked into the pore structure of the ceramic.

2. Puzzled - why would the amount of leaching from silver in a filter increase over time? And how would changing the filter regularly help, since the silver in the new filter will also leach? 

3. I stumbled on the "perfect" solution for this silver issue. Doulton has an EWC pre-filter cartridge which is supposedly based on USA KDF system. I did a quick read on KDF and one highlight is that it inhibits bacterial growth without silver...! Having said that, I realised it is a pre-filter, meaning to say it will still go through the main ceramic filter with the silver. 😕 It sounded promising for awhile though. Any thoughts on this KDF business? Only downside is, I doubt it removes fluoride. http://www.thewaterexchange.net/what_s_kdf.html

 

4. Using the Doulton filter (Sterasyl ceramic) as an example, how much water approximately would one need to drink to consume e.g. 10g of soluble silver (or maybe not even drink, if say you wash your hands with it)? 

5. Does silver pass out of the human body...? I'm sensing that it doesn't. 😐

Dear Paloma,

1. The value of 0.1ppm as given in the previous post refers to concentration of dissolved silver in drinking water. I suspect the 0.07% quoted in the Arkwater webpage refers to the amount of silver in the filter element i.e. if the filter element weighs 100g, silver will take up 0.07g. Therefore, we are not comparing apples to apples and it becomes meaningless to compare 0.1ppm to 0.07%.
   
2. Actually, I made the statement based on my experience in many applications, including outside the topic of water. Any material will wear and tear over time, both mechanically and chemically, the latter possibly due to attack by other chemicals e.g. chlorine which is a pretty aggressive compound.
   
   As the bonds within the material break down, anything held within e.g. silver will be released. As a material ages, more bonds will be broken, releasing more stuff.
   
   Yes, you are right, a new filter will leach silver but an old filter will leach even more.
   
3. KDF (also known as redox) filters are designed to remove lead, chlorine, hydrogen sulphide and guess what, fluoride too. When combined with other filters e.g. activated carbon, they seem quite effective at removing a good variety of pollutants. I personally have not done any experiments on them but they look promising.
   
4. Assuming the 0.07% does not apply here, if you base on a concentration of 0.1ppm silver in your drinking water, you have to drink for 70 years (2 litres per day) exclusively from that silver impregnated filter before you drop from argyria or silver poisoning.
   
5. The WHO guidelines on drinking water listed silver retention in humans and animals to be 0-10% which is pretty low.

All the best in choosing your filter!

Silver and magnesium in water: benefit or concern?

Dear Chen Ko


Hope all is well with you in the midst of semester and festive busyness. I see from your blog that your workshop was last Sunday, I hope that went splendidly!


 I do not know if you would be able to spare the time for a favour, regarding the questions I sent you on 2 January. The reason being my unforeseen need to make an informed decision about the water filter by next Monday, given some circumstances that have arisen. My residence includes young occupants, so I hope to be as careful on this choice as I can too for their sake.


I am incredibly sorry for any trouble and inconvenience my request may cause to you; I am truly appreciative for your generous professional insights this while. Allow me to say how these have really enlightened my understanding and shaped my considerations to date. Would be extremely grateful to hear from you if you could, even if otherwise I do understand. Warmest wishes to you and all of yours always!


Here are the two questions again:

1.     The Doulton filter (Sterasyl ceramic) is silver-impregnated ceramic. I understand the purpose of the silver is to disinfect and filter the drinking water. I expect that a presumably (and hopefully) small but unknown quantity will invariably enter the filtered water. I also read that silver is naturally-occurring around us... but drinking it daily in the long run may be quite another matter. I drink about 2.5-3.0 litres of water a day on average. I'm concerned about the accumulation of silver in the body, or if this taxes the kidneys/liver unduly.

So really – how safe is silver-impregnated water filter media for adults, infants and children? Or – in the best-case scenario – does the silver not leak into the filtered water at all? There may be scary consequences like argyria to consider for heavy water drinkers perhaps...


Some of the links I read on Silver:
http://www.who.int/water_sanitation_health/dwq/chemicals/silver.pdf


http://www.watertechonline.com/effects-of-silver-in-water/


http://www.silverhealthinstitute.com/silver-in-drinking-water/


http://www.silver-colloids.com/Pubs/dark-side-rebutal.htm


 
2. Of interest too was this new water filter I came across called Best Water Technology BWT (website here). They add magnesium to their filtered water, and this seems advantageous as magnesium is important for good health and most people have a deficiency despite it being available through food. From my reading of the various sites (including those above) it even seems that adding in magnesium to your water is still safer and better than silver – I could be wrong though.


If I recall right, you don't advocate stuff being added to drinking water or its nature being changed (e.g. alkaline water). Given all the touted benefits, would you say this for magnesium too?


Some of the links I read on Magnesium:
http://apps.who.int/iris/bitstream/10665/43836/1/9789241563550_eng.pdf


http://www.lifeextension.com/Magazine/2007/2/report_water/Page-01
 
Yours faithfully
Paloma




Hi Paloma,


It has indeed been a busy time for me, attending to many other commitments outside the topic of water. Sorry to have missed out your questions.


The workshop last Sunday had been a very interesting discussion as I got to meet artists, activists, hobbyists rather than the usual academics, regulators, industrial people and vendor types that I associate with. I will probably post something about it when I have the time.


Silver
This element has been very popular in the past years as part of water filter elements (no pun here)... silver impregnated ceramic candle, silver impregnated activated carbon are the more common ones. The theory is silver has claims to biostatic (stopping microbes from growing) and biocidal (killing microbes) effects. Therefore, it can prevent unwanted microbial growth on your filter elements. Look at it this way, instead of removing bacteria from your water, your filter is now adding them into your treated water.... Yucks!


A few thoughts about silver:

1. Elemental silver (the one in your silver coin and jewellery) is pretty insoluble in water so there is no issue of it being toxic this way.
   
2. But what about the silver in my water filter??? In this case, silver is typically applied as silver nitrate (silver nitrate is very soluble!) solution into wet ceramic clay homogenously before the whole mixture is fired in a kiln. This should lock the silver within the ceramic matrix in the finished product. However, various tests have shown that the silver can indeed leach out into water over time. Still, the concentrations of silver in water are very low - ppb (parts per billion) levels or less.
   
3. Back to the biostatic and biocidal claims.... Apparently, these claims are still not well established. Opposing studies have shown that adding silver does not make the filter any cleaner in terms of microbes.
   
4. WHO does not have a guideline value for silver in water as people do not get silver poisoning (argyria) from drinking the normal sources of water though it did mention that the use of silver for its biostatic and biocidal properties may elevate its concentration in water significantly. Hence, WHO did use a nominal value (taken from EPA?) of 0.1ppm (parts per million) that should not be exceeded.
   
5. What about NSF/ANSI certification (1, 2, 3)? One of the requirements for certification of a filter under this scheme requires that it does not leach harmful chemicals into the water. Unfortunately, silver is NOT under the list of chemicals tested since it is of such low priority (in terms of hazard or frequency) as a water contaminant.
   
6. I myself have water filters containing silver for the occasional use out of Singapore. But what if you are using regularly 24/7 for years?

My take
Based on the current literature, silver impregnated filters are probably safe to use. You have to ingest LOTS of soluble silver (say 10g) to suffer from argyria. Though the leaching of silver from a filter may increase over time, you are supposed to regularly change it anyway.


But since you are concerned enough about this issue to write to me and do research, you probably want to be more proactive. Therefore, I suggest that you send samples of treated water to a commercial lab for verification of the silver concentration. Is it less than the nominal value of 0.1ppm? Depending on how often you change your filter, you may want to do this every quarter or half year.

Figure: My favourite kind of silver

Magnesium
Magnesium is a vital mineral in our bodies, contributing to controlling heart rhythm, blood pressure, enzymatic activity and others. Its daily requirement is about half that of calcium.


Together with calcium, it also contributes to hard water. No, not the type in which your knuckles get hurt when you try to punch hard water. Instead hard water is well known in industry to cause problems in scaling. It also causes a similar scaling problem when you bath using soap and hard water.


Nevertheless, if you are a fish farmer or aquarium hobbyist, the health of your fishes (and other aquatic organisms) depends on a minimum amount of magnesium.


In recent years, some water ionisers (alkaline water) are selling on the fact that their machines add magnesium


A few thoughts about magnesium:

1. WHO does not view it as a health concern! There is no guideline value for it or for hardness.
   
2. Magnesium deficiency in humans in developed countries is not common, certainly not in Singapore.
   
3. A normal diet (nothing extreme) should give an enough supply of magnesium. I am not even talking about supplements. Nuts and milk have it!
   
4. I did not see the amount of magnesium added into water by the water filter in your link. Will you be inadvertently overdosing yourself if your only source of water is from the filter? Since magnesium is connected to many vital functions, it can just as well adversely affect those vital functions. It also has laxative effects!
   
5. Therefore my answer is NO, I don't see a need to have a machine to add magnesium into my water. I certainly do not want to overdose myself either.

Figure: My preferred sources of magnesium