To fill the reservoir completely you need 75 litres of water and there are a couple of ways to fill it.
Moti-Lab is fitted with two hozelock type attachments and you can simply attach a hose and turn the water on (make sure the outflow taps are closed). These attachments also act as overflow points (and eureka jars) so once full it will begin to overflow and you can turn the water off. This should take 5-10 mins depending on water pressure, for a video of this please click here
You can always get the kids to fill it with buckets of water from a tap.
Top Tips: You can turn filling with water into a mathematical / engineering exercise.
If filling with a hose you can time it and work out the flow rates of water from the tap, get the kids to estimate the time it will take to fill and test their guesses, how will the changing the rate of flow from the tap change the time it takes to fill?
If filling with buckets do some simple maths, estimate how many buckets will it take to fill the reservoir and test it. How much on average was in each bucket? If 4 children are filling it how many buckets will they each need to pour? There are loads of ways to bring maths into this exercise.