Saturday, August 17, 2013

Help! My rainwater harvesting system (RWHS) is not working (well)!

Further to my earlier posts on rainwater harvesting (RWH), I thought I should also present some possible problems faced by the rainwater harvester lest the reader thinks that rainwater harvesting is a big bed of roses. Nevertheless, I stand by my proposition that RWH is the best source of domestic water in rural/developing countries as long as you are living in a sub-Saharan climate.

These pointers are based by my experiences gained from my RWH projects so they are by no means exhaustive. But then again, RWH is not rocket science. As long as you exercise some common sense, do some basic research and you are on your way. Teething problems? Of course you will have them but nothing even close to life-and-death or that cannot be solved with hard work and ingenuity. "Improvise, adapt, overcome" If this motto is good enough for the US Marines, it is good enough for us.

Back to my pointers.

  1. A first flush diverter (FFD), roof washer or whatever-you-call-it is mandatory. It is basically a device to divert, filter or remove the first batch of rainwater from your roof - also the dirtiest part of the rain. Some people advise the first 5/10/15/(put your favourite number here) minutes of rain to be removed. Anyway, we tested the water quality from our FFD vs. the rainwater collected throughout the entire duration of the rain and no surprise, the FFD turned up significantly dirtier for almost all the water quality (WQ) parameters.

    Moral of the story: don't skim on your FFD/roof washer. Remember the old adage - penny wise, pound foolish.
  2. We tested out about 14 WQ parameters e.g. pH, conductivity, turbidity, nitrate, chloride, coliform, E. coli, hardness, alkalinity on rainwater itself, FFD water, final treated rainwater and compare them against PUB WQ from their water treatment works (no longer available on PUB's website but you can refer to their drinking WQ report for 2012) The parameter for final treated water that half the time did not meet PUB's guidelines is pH. Acceptable range is 6.5 - 9.5 while we got an average of 6.6 with a few data points below 6.5.

    No big deal actually for drinking (no, we didn't drink the rainwater though) but a small consideration for washing of metal parts e.g. car. Corrosion could be enhanced by acidic waters.
  3. Like the FFD, a vital piece of equipment is the strainer at the top of the downpipe (joining the gutter to the tank). If you place your RWHS in a well vegetated area like we did (in a garden), you will get lots of leaves, twigs and unidentified stuff trapped there in rainy Singapore. Clean it regularly or you will find your system clogged up or worse, a hot bed for mosquito breeding.
  4. Treat your rainwater treatment train (filters, UV plus whatever purification device) like your car - check them, clean them and change them when necessary.

    Case in point. UV disinfection is simple to install and use. No chemicals are needed. Just plug into a power source and presto. Right? No really... you  have to check the UV lamp regularly for fouling and clean it if fouled. A fouled lamp does not disinfect well. Ultimately, the lamp will gradually lose its intensity and you have to change it... remember pennies and pounds.
Good luck, folks!

Figure: The PVC portion jutting down from the tee forms the FFD

Wednesday, August 14, 2013

New publication on water quality monitoring in tropical ponds

This just came out hot from the press, published by CUGE (Centre for urban greenery and ecology). I am one of the contributors.

Title: Guidelines on Water Quality Assessment and Management for Tropical Ponds

"Guidelines on Water Quality Monitoring for Tropical Ponds sets out recommended standards for pond water quality for key parameters with reference to empirical measurements from 59 ponds across Singapore. It explains how to use water quality monitoring results to diagnose water quality concerns, and outlines a range of associated management strategies for addressing water quality issues in tropical ponds."

This guide is basically for tropical freshwater ponds. And it is geared towards assessing and managing the problem of eutrophication in ponds. No surprise since eutrophication happens to be the dominant problem in Singapore ponds with most under the jurisdiction of Nparks.
Of particular usefulness is a set of water quality guidelines e.g. salinity, pH, turbidity, total nitrogen, total phosphorus with qualitative and quantitative limits. This provides a useful benchmark for pond managers to determine the health of their ponds.
This guide discusses several management strategies to deal with eutrophication e.g. chemical treatment, wetlands, dredging, filtration.

Overall, it is a great introduction to the world of pond water quality, especially for  park managers who are familiar with plants and landscaping and clueless about water quality.

Monday, August 12, 2013

Do we actually have our own drinking water standards?

Perhaps not well known but Singapore has its own set of drinking water standards. This may be a result of the frequent mention of WHO as the sacrosanct authority on water quality (WQ) by the our authorities when it comes to drinking water. (Of course, our OWN standards are based on WHO standards with some modifications.)

Here goes:

WHO, IWA (International Water Association) webpage, NEA webpage
The above basically covers about 100 WQ parameters and their limits in drinking water. PUB has published their drinking water quality reports (2011 is no longer available online, 2012) based on testing for these parameters.
2. Code of Practice on Piped Drinking Water Sampling and Safety Plans

Essentially speaking, anyone who wants to dabble in his drinking water ought to go through these 2 documents to understand what is going on besides knowing how to turn on the tap and have water coming.

Wednesday, August 07, 2013

More recognition to grey water recycling!

Grey water (1, 2, 3) recycling has always been a less glamorous cousin to rainwater harvesting. After all, rainwater is clean water for drinking, bathing, cooking... all important processes for our health and well-being, while grey water is wastewater best kept out of sight and mind... as long as someone else is taking care of its disposal.

News update: Water is water is water (no typo here) by whatever name. The only difference lies in the "impurities" in the water, hence giving rise to black water (toilet bowl), grey water (sink, laundry, bath), yellow water (urine only), dark grey water (kitchen sink, diapers laundry). All water is intricately connected in the water cycle - both natural and human. In other words, rainwater or any other "clean" water can come from grey water. Therefore, it pays to conserve (read recycle) and handle your grey water properly.

It is therefore great news when I see that PUB has added a section on the guidelines of grey water recycling in Singapore.

1. Alternate sources of water
On this page, rainwater and grey water are officially recognised as alternative sources of water, not just at the national level or at the residential/individual level. I have written about rainwater harvesting in an earlier post.

2. The document itself

Some highlights
  1. It goes without saying - no potable use. But irrigation and general washing are also forbidden. Why then do you recycle grey water???

    Well.... it can only be used for toilet flushing and as cooling tower make-up water.

    Personally, depending on your treatment process, grey water can even be made potable. Even with simple treatment, its water quality can be made adequate for general washing and irrigation.
  2. As for rainwater harvesting, grey water recycling must follow PUB's standards for fittings and code of practice for water services, as well as NEA's standards for prevention of mosquito breeding.
  3. Raw grey water should not be stored for more than 24 hours. This IS reasonable as any time longer will lead to anaerobic conditions and foul odours.
  4. Treated grey water should not be retained for more than 72 hours. This DEPENDS on the type of treatment. If the final water quality is that of drinking water, I am sure the duration can be stretched.
  5. Incidentally, there is no mention of WHAT type of treatment process you should use... Instead, whatever treatment must produce a water conforming to the water quality guidelines (listing the various water quality parameter and their limits) given in this document. This is immensely useful as previously, there were no such guidelines.
  6. And also very useful is the schedule for water sampling and monitoring e.g. testing for E. coli and coliform should be done monthly.

 Figure: PUB guidelines for treated grey water quality

Figure: PUB sampling regime for treated grey water

Source of the above 2 figures: PUB document (

In conclusion, I believe we are on the right track on publishing such standards for grey water in terms of its water quality and testing schedule. I hope more developers and individuals will take up the challenge to implement grey water recycling on a residential or building scale.

Natually, there is much more to be done. E.g. I am impressed when habitats use plants not only to clean up grey water but also to provide edibles for their inhabitants. Bananas can be clearly seen in my previous posts (12) illustrating this concept in an Earthship.

Figure: Bananas, anyone? (Source:

Tuesday, August 06, 2013

More power to rainwater harvesting in Singapore!

Hi folks,

It has been a long while (Mar 2004 till now to be exact) since Dr Tan Cheng Bock (Singapore presidential candidate in 2011) advocated water conservation by implementing a rainwater collection tank to water his garden despite the illegal nature of such an act before that time. See Straits Times article below (dated 16 Mar 2004).

Source: Straits Times 16 Mar 2004

Before 2004, collection of rainwater was forbidden except for the use of pails in residences. Building a rainwater tank was strictly a no-no. Rationale: rainwater was a property of PUB acting in the best interests of the nation in water conservation and rainwater collection via the canals and drains that ultimately flow into reservoirs (technically, only two-thirds of the land area here is available for rainwater catchment so not all rainwater is channelled into reservoirs). Yes, you are expected to let the government handle YOUR water needs. What a mentality...

Since then, even though not widely known, rainwater harvesting has been legalised for households as long your rainwater storage tank is no bigger than 5x2x2m (or you will have to pay a levy for wastewater treatment) and your rainwater is for non-potable uses. Institutions and companies will have to apply for a permit if they want to implement rainwater harvesting. Still, many got their permits e.g. Changi Airport (1, 2), Nanyang Polytechnic, Poh Ern Shih Temple.

But now, it is official!

Details are now more clearly spelled in PUB's website:

1. Alternate sources of water
This page also includes grey water recycling (I will cover this in a separate post) which is now officially recognised too! How exciting!

Some highlights:
  • Owner/developer/QP/PE can submit an application to PUB for rainwater harvesting.
  • Please note that rainwater is only (and still) for non-potable use.

More details can be found in this document.

Some highlights:
  • Not surprisingly, rainwater harvesting equipment has to comply with the Code of practice for water services and the fittings must follow the standards under PUB.
  • What are your non-potable options in the use of rainwater?
    • general washing
    • toilet flushing
    • irrigation
    • Sorry, no bathing and washing of hands... (and I though that rainwater is supposed to be good for your hair)
  • Excess rainwater should be allowed to overflow into drains which of course goes back to becoming the property of PUB.
  • Don't forget the other governmental big brother, NEA. Your rainwater system also has to comply with NEA's guidelines, especially concerning mosquito breeding.
      • Guess what... gutters are now allowed (though "discouraged") for rainwater harvesting provided they follow the guidelines given here.
      • The same rainwater is not supposed to remain for more than 7 days in the storage tank (translated as residence time to the engineer reading this).
3. Drainage handbook
A big document - 82 pages. More for further info and background.

My take
Well and good. People should have a role in conserving and utilising this precious resource. No doubt, centralised rainwater harvesting by PUB is indeed useful. However, the people need to be allowed more freedom for initiative to take care of themselves and the environment.

Personally speaking, rainwater is really clean water. The possible contaminants will be dust and dissolved gases and whatever that adds into the water by the collection system e.g. bird droppings, dead insects. After some minimal treatment, rainwater is certainly potable. As mentioned in a previous post, I strongly suggest rainwater as compared to other sources for consumption rural/developing communities overseas.

Figure: Source: Straits Times c2003. Rubbish choked water in Muara Baru, north Jakarta. I don't know about you but I prefer to get my water from the rain rather than from surface water like this.