Lesson Plan Title: Water filtration model Concept / Topic to Teach: How water is filtered naturally through the layers underneath the ground, and how to replicate/ represent this on a smaller scale. Target audience: Primary school: 3 rd to 6 th class and Secondary: all years. General Goal(s): Firstly to understand the natural process groundwater goes through and to appreciate how long this process can take. Then to appreciate how outside impacts (e.g. pollution and over-abstraction) can affect this source of freshwater. Specific Objectives: On a practical level: how to make the filtration model To illustrate how water is cleaned in the natural environment To reveal the dynamics of water i.e. where it goes when it falls on the ground To show how modern water treatment uses similar materials (sand/ stone) to those which clean water in the natural environment Seven Step Link: All
Required Materials: One 2 litre bottle of water with the label taken off and the base cut off and a hole made in the lid One 2 litre bottle of water filled with dirty water Two 1 litre jugs A handful of grass/ moss Two handfuls of pebbles Two handfuls of builders sand (play sand doesn t work) See pictures below Figure 1. Showing all the materials needed to complete the water filtration model.
Preparation Level: High Student s pre-requisite knowledge and skills: An understanding of the water cycle would be beneficial. Anticipatory Set (Lead-In): The use of the water filtration model ties in with a talk on the sources of water, water treatment and the general movement of water. This would be a talk designed to provide an understanding of where our water comes from and how it ends up in our taps. The aim is also to develop an appreciation of the journey water has to take in order for us to be able to drink it. Finally, the model itself contributes to an understanding of where all our water goes e.g. all the rain falling on the ground. Since the filtration model fits in with a talk on sources of water, you might already have discussed the water cycle and where our drinking water comes from. Then you can pose a new question: What happens to all the rain that falls on the fields, and the ground outside (its good if there s a view onto fields), where does it go? This is as opposed to their familiar view of all the rain falling on top of the mountains and turning into rivers etc. from the water cycle. You will be met with lots of answers, and the beauty is that they re all fairly much correct because so many things happen to groundwater. I tend to say: you re all right, and that right underneath our feet there is loads of water all moving in different ways. There are rivers and lakes far underneath the ground, and some water is moving slow and some is moving fast, and some bursts up as springs etc. The filter then shows one of the ways that water acts when it is in the ground.
N.N.B. It takes about 10/ 15 minutes for the dirty water to become clean by going through the filter, so this is why it has to be part of a bigger talk. The way to do it is at the start of the lesson, to get two pupils to start the filtration process. I mention to the rest of the class that I ll come back to this particular experiment in a while, and then come back to it in a few minutes after I have discussed other aspects of water and built up to it. Step-By-Step Procedures: I make the water filter at home and the students just run the dirty water through it until it is clean. This is because it can be messy and takes time anyway. To make the water filtration model: Cut the base off a 2 litre bottle, it can be sharp afterwards so you have to give it quick sand down with something to blunt the edges in case pupils holding it cut themselves. Then put a round hole in the lid about 6mm in diameter. You might have your own way, but I found the best was to heat something metal like a drill bit and it goes through the plastic real easily (that s the hardest bit!). Otherwise it s hard to make a hole in the lid at all. Put the lid back on the bottle and put a small bit of grass/ moss in the bottom to stop sand falling out. Then fill about a third of the bottle with building sand. Fill the next third with pebbles. Fill almost the last third (don t go right to the top) with grass/ moss.
In the classroom: Get two students to be responsible for the filter until you get around to talking about it and/ or the water starts coming out clean. One has to hold the filter over a jug while the other pours in the dirty water. The water has to go through a few times until it is clean. So every once in a while the jug that the water is dripping into has to be replaced quickly with the second jug, and the water that has filtered through poured back into the filter. While you are talking, you can keep an eye on the progress of the filter, and remind them to change the jugs if needed. Eventually, the water coming out of the filter will become cleaner, and this can be shown to the class compared to the remaining dirty water in the bottle. Figure 2. a) Showing the 2 litre bottle with the base cut off and the lid with a round hole made in it, and b) the 1st layer of the filter (a small amount of grass/ moss)
Figure 3. a) Showing the 2 nd layer and 3 rd layer (sand and pebbles), and b) showing the final layer (more grass/ moss). Figure 4. Showing the water filter placed in a jug, with dirty water about to be poured through it.
Adaptations for students with learning difficulties: The filtration model is a very visual exercise and would work for nearly all students as the end result is simply comparing very dirty water and clean water. It would be difficult to adapt it anymore. Extensions (for gifted students) Something that could be done but I have not tried yet would be to let a few groups of students create their own water filters with possibly smaller bottles. Only recently I have seen a similar version of this water filtration model done by the Irish Peatlands Conservation Council (IPCC) at their workshops. They call it: bog in a bottle and although it is not a water filter, it tries to represent the many layers of the bog. In the same way the water filtration model essentially gives students the image of looking at a slice through the ground and showing its many layers. Links to other subjects Compliments and touches on many aspects of SPHE, science, geography.