We Built a Miniature Drinking Water Treatment Plant – Learn About Creating Clean Water

Trevor English

Being able to turn on your tap and get fresh clean water takes a lot of work, and I have built a miniature drinking water plant that will hopefully help you understand. Outside of Interesting Engineering, I, Trevor English, am a civil engineer, with a specialty in water systems. I built this miniature water treatment plant with a team of two other engineers, and hopefully, it can help you understand how to turn dirty river water into clean drinking water.

watertreatmentsetup6875d[Image Source: Trevor English]

To begin the project, my team and I began with 55 gallons of incredibly murky river water. The goal was to clean the water of all particles and kill off any bacteria or pathogens. The end product was completely clear and safe to drink water, and here's how we did it.

The key components of drinking water treatment are processes called coagulation/ flocculation, sedimentation, disinfection, and filtration. If you are curious about all of the ways that these processes can be customized in different systems, leave me a comment, but for this post, I will do an overview of how the system I designed works. To get us started, take a look at a video I made walking everyone through the miniature treatment plant.


Coagulation/ Flocculation

The first step of treating the water is to remove all of the clays, silts, and dirt particles suspended in the water. The river water we started off with was very brown, in fact, it was hard to see more than an inch down into the holding tanks. To remove the particles, we added a chemical called Aluminum Sulfate (Alum) which in a process called coagulation/flocculation, which basically causes all of the tiny dirt particles to stick together. We built a rapid mix tank (coagulation chamber) where the water and chemicals were stirred together, which then outflowed into a basin that allowed these formed particles to settle. You can see the rapid mix chamber below.

coagulation basinWe hot glued 2 washers to a screw and attached it to a motor. If it ain't broke, don't fix it [Image Source: Trevor English]


The particles in the sedimentation basin would very slowly fall to the bottom. At this point, a water droplet would have been in the system for around 2.5 hours. From here, the water would flow over a weir. The cleanest water is on the surface, so the weir made sure that only clean water moved on to the next step. The water leaving this basin looked very clear, and virtually all sediment had been removed from out alum addition.

weir flow basin[Image Source: Trevor English]


After flowing over the weir, it would travel through a short tube into what is called a plug flow reactor. This is a little bit like a maze, and its sole purpose was to increase the amount of time water spent in the system. We added a select concentration of chlorine, based on preliminary bacteria testing to make sure we killed everything off, called disinfection. Believe it or not, this chlorine we added was just a solution of off the shelf bleach and water, and it is perfectly safe when added in small amounts. If you're in the US, there is likely chlorine in your tap water right now. Water spent about 1 hour in the plug flow reactor where it would then flow to the final step in treatment, the sand filter.

plugflow964d9[Image Source: Trevor English]

Sand Filter (Filtration)

The sand filter is exactly what it sounds like, a basin with different grain sizes of sand that caught any other particles or contaminants that weren't picked up in previous treatment. Sand filters are used in virtually every water treatment plant as they are the most effective way to clean water.

Disregarding bacteria, you could actually treat water using only fine sand, but you would have to clean out the filter a lot. This is exactly how mountain springs work. The sand filter was by far the longest part of the process. A water droplet would take upwards of 5 hours to flow through here.

sand filter outflow[Image Source: Trevor English]

Final Clean Product

Our outflow was rather rudimentary, but it did the job. We tore off a piece of t-shirt that directed the water into a small holding basin. From here, we used a small pump that took the clean water and moved it into another 55-gallon drum, that started off empty.

working treatment[Image Source: Trevor English]

We started with exactly 55 gallons of dirty river water. Our goal was to end up with 40 gallons of clean water. The final product was 42 gallons of clean drinking water, which could have been increased if we eliminated some of the inefficiencies and water loss zones in the small system.

Here's the best part

This system is completely portable, and could be transported and used virtually anywhere in the world. It would require some basic chemistry knowledge to get the chemical additions right, but if you wanted, you could treat water for a small village using this miniature treatment plant. I wouldn't reccomend doing this without proper foreknowledge, however.

If you have absolutely any questions about more specifics on the system and how we tested and calculated everything, please leave a comment below and I will answer them. Feel free to ask other general water treatment questions as well, I am here to answer them!

Exact numbers: In total, we added 10.4 mL of 6% bleach, which worked out to a final concentration of around 3.15 mg NaOCl in the final treated water, within standard in our area. For alum, we added 62 mL of 10g/L Alum solution ever hour. This worked out to a total of about 1.3 L of Alum solution needed. The final testing flow rate was about 14 L/hr or 4 mL/min. All of these values were calculated from initial bacteria testing on a petri dish as well as flocculation testing to see where the optimum flocculant dosage was.