How It Works

This post was transferred from my old blog. See the original post (with comments) at:


I spent my first three months here in Malawi working with gravity fed water systems.  Taking advantage of my new cartoon drawing kick, I thought I’d take a few minutes to explain how one works.

The pictures I used are from a real gravity fed system, but obviously the cartoon schematic below is not accurate or to scale. I just drew it to try to show all the fundamental elements of a system, and how they fit together.

How it Works

1. The Intake

There are two major types of intakes: river intakes and spring intakes. A river intake involves damming a small river. Water pools behind the concrete dam, and then flows into a pipe. Excess water overflows the dam and continues down the river.


A river intake on the Sankhulani scheme, shown with Mr. Alizeo (repair team member) and Mr. Utumbe (government water supervisor).

A spring intake involves finding a spring right where it bubbles up on the ground, and capping it to protect it from external contamination. All of the water then goes into a pipe and down into the system.

image A spring intake on the Sankhulani scheme.

2. Screening Tank

Sorry, I don’t actually have a picture of one of these. The basic purpose of a screening tank is to get sediment and other debris out of the water before it goes to people’s taps. It’s been a while since I’ve seen one, but this is a (very) rough approximation of how it works.

Screening Tank

A “schematic” of a screening tank. Water flows in one side, debris settle to the bottom, and water flows out the other. A dividing wall in the middle eliminates water flow at the bottom of the tank, ensuring that debris settle.

3. Sedimentation Tank

On most of the scheme’s I’ve worked with, I don’t think there’s really any design difference between a sedimentation tank and a storage tank. A sedimentation tank is basically just a big tank where any sediment that makes it past the screening tank can settle to the bottom.

image Mr. Friday (Sankhulani scheme repair team member), cracking open the hatch on a sedimentation tank.

4. Break Pressure Tank

Water flowing downhill can build up a lot of pressure. Excess pressure can damage taps, break pipe connections, and cause all kinds other problems. That’s why break pressure tanks are used to reduce water pressure. They’re very simple. Water flows into a concrete tank, hits the far wall, sloshes around a lot, and then flows out the other side. Goodbye pressure.


Mr. Alizeo and Mr. Utumbe opening up a break pressure tank. The concrete slab in front of the tank has a valve under it, in case you want to shut off water flowing into the tank. The top pipe on the right is an overflow pipe, and the bottom one is an outlet pipe (for draining the tank before cleaning).


The inside of the tank. The pipe on the right is the inflow, the pipe on the left is the outflow. Notice that they’re not directly aligned, ensuring that the water will have to slosh around in the tank before flowing out. The pipe at the top of the picture is the outlet pipe for cleaning.

5. River Crossing

Most gravity fed water systems have many river crossings, which are like Achilles’ Heels for the systems. During heavy rains, trees frequently wash down the river, knocking out the pipes. When the pipes get knocked out, whole sections of the system lose water, and repairs usually can’t be done for months (until the rains slow down). Without water, people stop paying monthly contributions, meaning that there’s less money available to do the repair when the time comes. Dealing with river crossings is definitely a tough gig for scheme management.


A river crossing. (Note: crossings are supposed to be done with galvanized steel pipe to reduce the risk of washout, but once that pipe gets washed out, it often gets replaced with PVC, increasing the risk of a washout next year.)

6. Air Valve

Although these systems are powered by gravity, water still sometimes has to flow uphill. (See the first schematic). When it does, there is a risk of air getting caught in the pipe. If air does get caught in the pipe, it essentially gets trapped (since it can’t flow through the water), builds up pressure, and blocks flow. It can sometimes also burst the pipe.

To prevent this, air valves are used to let the air out of the pipe. I’m not sure how they work exactly (I’d love to take one apart some day, but the chance hasn’t come up) but somehow they allow air to exit the pipe but not water.


Mr. Friday inspecting an air valve that’s obviously broken. This picture gives a good idea of why it’s broken: too much water pressure. The valve pretty much just flew off, but we found it close by. See the next picture for Mr. Friday’s clutch repair strategy.


All better, assuming the water pressure never gets strong enough to knock these rocks off. The pipe at the bottom is the main line for the system. The riser coming off of it is leads to the air valve.

7. Storage Tank

Think you can take a guess at this one? Well, you’re right. A storage tank is pretty much what you’d think it is: a tank for storing water. This helps regulate water pressure in the system, and also ensures that taps towards the end of the line have water even when flow from the intake is low.


There it is. A storage tank. The pipes coming out of the top allow air to get out when the water flows in (and vice versa) preventing air locking.


Inside the storage tank. One of the echoier places I’ve ever been.

8. Water Tap

Finally, a water tap. The point to these systems. Where the magic happens.

The big gravity fed schemes in Thyolo, where I was working, have between 80 and 100 taps each. This gives communities way denser water coverage than drilling boreholes (one borehole with a pump costs around $10,000, so you have to be sparing with them) meaning women and children have to spend less time walking each day to fetch water. The water is also usually safer than what’s available form traditional sources.

imageA water tap on the Sankhulani scheme. To give an idea of scale, the intake for the system is on the far side of that forested mountain in the background. To further that idea of scale, this tap is only about halfway down to the end of the system. These things are big.



A water tap on a smaller system in Thyolo, this time with community members posed for a photo. Nice.

Well, hope that was interesting. Gravity fed systems are an example of a pretty simple technology (just simple pipes and concrete) that can make a pretty big difference in people’s lives. Keep in mind though, these things need to be maintained. Imagine cleaning all those tanks, fixing all the breakages, searching along kilometers of underground mainline every time there’s a leak. And it’s all up to community volunteers. It says something about the strength and work ethic of Malawians that these things ever keep running.

40 responses to “How It Works

  1. Pingback: “Appropriate” Technology « Hooked on Mangos

  2. Pingback: Pre-departure « In her shoes

  3. Your desire to become certified will do lots for both your personal
    reputation and the salon that employs you, so take care of this important credential now.
    Semiconductor chips are subject to an etching process that exposes the chips to corrosive gases.
    The coloring initially comes from bronzers, until DHA has time to
    react with skin and gradually darkens dead skin cells.

    * You need not apply spray based tanning products with
    your hands and hence there is no possibility of streaks or missed patches.
    Step Nineteen: Remove “palm tree” tanning
    stickers from my daughter’s hair (and other body parts).

    If you got sensitive skin, it’s better to remove hair a couple of days before to
    avoid rashes. The correlation between tanning and skin cancers such as melanoma has
    prompted many to preference fake tans. The high absorbent formula ensures that the lotion does not seem patchy or leave streaks
    of color. This may take time to register your
    business and obtain all the correct licenses.
    Your safety and the safety of the people around you will
    be tantamount when you have a Taser stored somewhere in your house.

  4. Today, people are aware about skin cancer causes and majority of people chosen natural tanning method to cure skin diseases.
    Later, you can apply a self tanner to your feet to give the right amount of color.

    This is because the spray tanning fluid complements and
    enhances natural skin tones and is therefore better
    suited to people with darker skin. This will
    help eliminate build up in the nooks and crannies such as armpit areas and behind the knees.
    Before apply the self tanner you need to make sure that you skin is completely dry.
    Peptides have been increasingly pure per customer demand.
    So, no more lying out in the sun for days, or laying in the tanning bed for
    days. Besides, consistent use of sunscreens
    could even cause Vitamin D deficiency. Even you can get sun-kissed
    skin all the year round. While applying the tanning lotion, you should always use the mat and gloves meant
    for tanning.

  5. The basis for a diagnosis will start with a thorough examination by your
    veterinarian. Redheads and folks with course hair
    will typically be higher shedders than blondes or those with
    fine hair. We live in a climate that gets hot and humid and there
    are many activities to choose from.

  6. If you are looking for the best way to file for extension electronically, then you should
    use IRS e-file. The price of an accountant may be
    fairly steep, and if the costs of starting your business are growing then the thought of this fee may
    put you out. Then you narrow down to your area of expertise (in this case accounting)
    and place and put in your keywords and press enter.

  7. Yes, fake tan can look really good when done properly but often by doing it our self’s and even sometimes professionally it can turn out bad and embarrassing.
    He still couldn’t believe that he was working for the woman everyone referred to as Mrs.

    Social studies have shown that men and women both view a tanned body as
    being healthier than a tanned body, but it is worth bearing in mind that if a sunbed is used
    for more than the recommended amount of time, there
    is likely an ugly truth hiding behind apparently healthy tanned skin.

  8. Their ringer t-shirt will be the type connected women’s clothing used mostly
    as their sports uniform. Another thing to think
    about are the flowers the bridesmaids will wear. Many people are interested in knowing these and
    thus, if one is looking to start a fashion website, all they have to do is to include this aspect to their portal along with pictures as well.

  9. The best part is you do not have to deny your sweet tooth using these quick weight loss diets.
    So possessing a spouse together with you on the diet
    will maintain accountability to oneself, to
    associate as effectively. These picnic spots and weekend gateways are spread along the borders ofthe city.

  10. You can really help most of your clients by helping them use financial statements as a basis for making better business decisions.

    They come to the picture even in divorce cases in order to establish compensation that is needed for
    child support or spouses. Every year, thousands of vacancies
    open up in the public sector.

  11. Any type of gold chain, ring, or earrings, can give someone
    a relaxed style, and also look very trendy for this season. Not only is Junior sized clothing not cut for a woman’s figure, it also shows more skin that we would like.

    Within the Wet Seal online store, you’ll find jeans,
    tops, graphic tees, sweaters, bottoms, dresses, active wear,
    outerwear, shoes, accessories, and intimates.

  12. Asia-Pacific Exhibition 2008 printing supplies more than 300 exhibitors of supplies, it also reflects the “337 Case”
    general supplies for domestic manufacturers is gradually dispersed cloud
    caused, general supplies in the market competition will become more intense.
    To reduce this feeling, simply take a clean feather duster or large
    powder bush and dust your skin lightly with a small amount of
    baby powder. People have very different types of skin, and the self tanning products you use will look different depending on this.

  13. Quite a few treatment centers impose as per the
    time required each meeting. During the treatment, the area is protected by
    using a dynamic cooling device that spreads cryogen onto the skin to cool the upper layer and facilitates
    you maximum comfort. The best secrets to great health is in quality, not quantity.

  14. Unlocks the Think Fast title and the League Grenade emblem.
    Compare free instant online moving quotes and pick the best moving company based on services & price.
    If you rely on outside sources for your accounting, it’s best to invest in an inventory purchasing software system that can analyze your inventory and let you know when it’s time to reorder of if you are overstocked.

  15. You stood up for the rights of all people of
    a great nation in combat, but unfortunately, you must continue to
    stand up for yourselves to ensure that the promises
    of being taken care of upon your return are kept.

    In Texas the penalty is 25% and in Georgia it’s 20%. ~ Relieving any person from liability to pay
    income tax .

  16. Emergency physician ultrasonography for evaluating patients at risk for ectopic pregnancy: a meta-analysis.
    First Response Early Results home pregnancy
    test is the most sensitive, cost effective, $12. The most popular influence of
    technology on health is weight loss.

  17. Yet he chose to ask me so many questions about how and why I do
    things, because he could see the profound insight I had built up due to going my
    own way with my own research and testing over the past 7
    years. Methods for baiting a hook – Step 5: Use them for fishing.
    If you are getting ready to go deep-sea fishing, there
    are a few things you might want to know about sea fishing bait.

  18. One more thing on which you need to pay attention to is fats and this is
    something that you should not be consumed in the large amount.
    Indeed, it has been found that men using HCG to lose weight have even better outcomes than female users
    in several instances. HCG diet materials stress the importance of sticking to this diet.

  19. Check out Movers review, it’ll assist you simply slim down the alternatives then choose many sensible movers.
    ” The easy answer to that difficult and (often) emotionally charged issue is that you need to determine how much stuff you will really need to take along to your new home. If you decide to pack them yourself, you can find an array of supplies to help you pack.

  20. FDA laser safety standards for identification, each 5-10 minutes, every 1 to 2 times will be able to achieve
    the maximum effect, general hair loss after three weeks there will be improved signs of immature hair growth hair loss
    site, in the course of treatment after three
    months, you can see the thicker and darker hair grow.
    Blow drying can damage hair as can vigorous towel drying as
    when the hair is wet it is more elastic and vulnerable to breakage.
    Warm water opens up the cuticle allowing you to clean the hair shaft, but if you use warm water to rinse your hair
    the cuticle will stay open allowing moisture in and
    the hair shaft to swell.

  21. Fruits and vegetables are naturally low in calories.
    The biggest reason they have for doing so is they often fail
    at their efforts to lose weight. This is a
    big benefit over other weight loss diets because
    the feeling of weakness, ranging from high to very high,
    is quite often experienced by dieters practicing other weight loss

  22. There is no such thing at the moment but there are goods that promise to stop additional hair loss and maybe restore some of the lost hair, if
    the follicles haven’t completely withered
    away. The platinum blonde is a much sought after persona, and the look, an elegant and beautiful one
    if carried off properly, is a much desired and much employed part of dressing up.
    You can get great results at a much cheaper rate by looking for hair transplant abroad surgeons.

  23. All you have to do is transport the items from point A to point B.
    ” The easy answer to that difficult and (often) emotionally charged issue is that you need to determine how much stuff you will really need to take along to your new home. People love to relocate to this place, as there are ample of opportunities for a person in Virginia.

  24. h – CG also resets metabolism rates and protects the healthy fat which cushions the organs and other tissues.
       Once you are on the calorie restricted
    diet and when the body demands energy, the HCG hormone will ensure that that energy is released from the stored fats
    and not from your lean muscle mass. It is a bit pricey, but is well worth the extra money.

  25. Many people talk about tax loopholes, understanding
    the details involving one of the IRS’s top tax loopholes enables you
    to speak or protest with confidence. Individuals
    and organizations, who find the procedure of preparing tax statements and
    filing them quite difficult, can opt for outsourcing tax return. ”John responded, “What should I
    do with your ashes.

  26. As well as students are liable to include the ways for which business are imposed to pay different taxes.
    As a law, you should determine if the IRS
    is open to negotiation to arrive at a compromise. Secure an order of payment(OP) from
    the assessors office, proceed to the realty tax section and
    present the OP with the latest official receipt (OR) and new tax declaration for new transferred properties.

  27. deck stains Colors

    2 bunches green onions, chopped with some green included.
    Would you like to advertise your fishing boat for sale.
    Anyway, after all that the judge abruptly stated that he found me to be an expert
    in my field and asked both attorneys if they had any objections.

  28. Hello, I think your blog might be having browser compatibility issues.
    When I look at your blog in Opera, it looks fine but when opening in Internet Explorer,
    it has some overlapping. I just wanted to give you a quick heads up!
    Other then that, excellent blog!

  29. I loved as much as you’ll receive carried out right here. The sketch is tasteful, your authored subject matter stylish. nonetheless, you command get bought an impatience over that you wish be delivering the following. unwell unquestionably come more formerly again since exactly the same nearly very often inside case you shield this increase.

  30. Regardless of your industry and business size, Facebook and Google+ are two of the Big Four
    social platforms that you can’t afford to ignore. There are various popular social
    media platforms like Facebook, Twitter and Linked – In; you need to understand the various channels and create your business profile accordingly.
    Controlling your time and energy and the zero’s on your paycheck is essential these days, and with this type of business you are able to.

  31. The hair follicles are not receiving the right balance of nutrients they need to grow.
    Consult with a veterinarian for the proper dosage based on the individual pig’s weight.
    Your hair protected the top of the head from the elements.

  32. The basis for a diagnosis will start with a thorough examination by your veterinarian. Consult with a veterinarian for the
    proper dosage based on the individual pig’s weight.

    However, pulling on a scab that was adherent to the skin usually dislodged the graft
    – often several days after pulling on a hair was safe.

  33. It is nice to know if you are pregnant when you are in the comfort of your own home.

    After all, they don’t call them guilty pleasures for no reason. The most popular influence
    of technology on health is weight loss.

  34. Celebrity garments can be selected for any time, gender, circumstance etc.
    Here are a few tips to prevent basketball injuries.
    Longer neck, long neck, high collar lining, there is
    a Painting in the United States.

  35. Good day! This is my first visit to your blog! We are a team of volunteers and starting a new initiative in a community in the same
    niche. Your blog provided us valuable information to work on. You have done a outstanding job!

  36. Paragraph writing is also a fun, if you be familiar with then you can write or else it is difficult to write.

  37. Just want tto sayy your arfticle is aas amazing. The clarity in your
    suybmit is simply spectacular aand i ould suppose you’re an expert oon this subject.

    Well along with yourr permission let mme to takle holld of your feed to keep updatedd
    with imminentt post. Thank yyou a million annd
    please continu the rewwarding work.

  38. Being overweight is the source of numerous medical conditions which necessitate long term attention but obesity also affects the manner we look at ourselves as well.
    Phenphedrine uses new proven acai berry reviews ingredients to facilitate weight loss.
    Originally, this type of” white meat” contains way
    more fat than fried beef ex. Therefore, it is not going to take my family out for
    dinner wearing my favorite nice red top I used to be able to control.

  39. Pingback: Burbank plumber

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s