The Lough in Cork is a shallow freshwater lake. It is roughly a metre deep and the size of four football fields. The water in the Lough comes from underground springs. It has an island in the centre that is home to a variety of wildlife and birds such as swans. Fish also live in the lake, there are Irish Carp, eels, perch and many more in the Lough. Many people visit the Lough every day to feed the birds, walk around it and play in the park beside it. In the past, people even used to ice skate on the Lough when it froze.
What is the problem?
Every summer our school takes part in a hurling tournament beside the Lough. We are usually tired and thirsty afterwards and as there are no taps nearby, we wanted to know if it is safe to drink the water from the Lough.
We thought the water might be dirty from all the birds, fish and other creatures that live there. We also believed that there might be bacteria and other chemicals in the water from all the people that visit there.
We did a survey of pupils in our school to see what they thought. 56 pupils thought it was safe to drink and 47 thought it was unsafe. We definitely had to do more work to figure out if it was safe or not.
How did we solve the problem?
We walked to the Lough and collected a sample of water. When we examined it we saw that it had small pieces of dirt floating around it and even though we couldn’t see any, we thought there might be bacteria as well. This would taste rotten and probably make us sick.
We decided to build a filter to clean the water and then boil the clean water to remove any germs and bacteria such as E.coli.
How does a filter work?
A filter should clean the dirty water by blocking all the dirt and only leaving the clean water through. Every layer of a filter should block different types of dirt from passing through to the next level. Eventually, only the clean water should come out the other side.
Did you know that filters are used to clean all drinking water before it enters your home?
For our filters we used:
- Gravel to block the big dirt particles.
- Sand or fine gravel to block the medium dirt particles.
- Filter paper to block the small dirt particles.
- We also decided to add some activated charcoal.
Just in case the charcoal left any bacteria or germs through we decided to boil the water. Boiling the water kills off any dangerous germs and makes sure that people wouldn’t get sick if they drank the water.
In our first design we placed a coffee filter inside a bottle and put layers of gravel, charcoal and sand inside the filter. This didn’t work.
Our first problem was that the sand was washed through the charcoal and the gravel and the water we collected was still dirty and full of sand. The second problem was that some of the water went down between the filter paper and the side of the bottle and wasn’t filtered at all.
We decided to make a new filter that wouldn’t have these problems.
In our second filter we put the coffee filter paper at the bottom of the bottle. This stopped water running down the sides. We decided to put charcoal at the bottom, sand on top of it and gravel on top of that. We put in a lot of sand to make sure that it wouldn’t wash away.
This time our filter worked and the water was much clearer when it came out. The problem with this filter was that it was too slow and only gave out a couple of drops every half hour. This was because the sand was too fine and we had too much of it to allow the water to pass through.
We decided to make a new filter.
In our third filter we put three sheets of filter paper onto the end of the bottle. This We put charcoal into the bottle first, we put fine gravel on top of it instead of sand to allow the water flow through it and gravel on top.
This time it worked perfectly and the water flowed through much quicker than the last filter because there was less filter paper and sand to slow it down. It still filtered the water perfectly though. One drawback of this design is that it needs three sheets of filter paper, otherwise it will leave small particles through. Another drawback is that the filter paper needs to be changed after 10 or 15 minutes as it gets too soft and starts to break.
This time we were happy with our filter and used it in the rest of the experiment.
How long do you think it took to filter 250ml of water?
When we recorded it, it took us 6 mins to filter 250ml of water with our third filter. It took us 2hrs and 30 mins to filter 250ml with our second filter. This was definitely too slow!
Did you know that 10-12 year olds should drink 2litres of water a day? If you were using our third filter it would take 32 minutes to get enough drinking water for the day.
If all 103 students in our survey wanted to drink a litre of water it would take 1,648 mins or 1 day, 3hrs and 28 mins using one filter!
We could give all 103 students a litre of water in 16 mins but we’d need to have 412 filters!
When we filtered the water we checked it for dirt. When it was clear we boiled it in a kettle to get rid of any leftover bacteria.
We then used a water testing kit to make sure that it was safe to drink. When we used the kit, it told us that the PH level was 6.5 which is perfect for drinking. There was no iron or nitrates in the water which was perfect for drinking. We then did a bacteria test and it showed no bacteria in the water. Finally it was safe to drink!
We found that drinking water straight from the Lough is unsafe as it is too dirty and may contain bacteria.
We found that filtering the water and using charcoal cleans the water and removes some bacteria but is still not safe enough to drink as there may still be bacteria in the water.
We found that boiling the filtered water removes bacteria and is finally safe to drink.