Summary A closed container with warm water and a small pot to collect the evaporated, then re-condensed, water shows how freshwater lakes are made from salty ocean water. Science content Earth/Space: Water cycle, Water conservation (2) Science competencies (+ questioning + manipulation + others that are in every activity) Questioning/predicting: predicting (1 up), hypothesizing (7) Evaluating: inferring (3 up) Lessons activity is in Water cycle Materials For each model (can use one per table group) sturdy plastic storage tub, roughly 30cm long x 15cm wide x 15cm tall small pot or bowl (that is less than half the height of the storage tub) 3 tablespoons salt, optionally divided up so students can add 5 drips food colouring cling film to cover the top of the tub with at least 5cm overlap (I found Glad wrap worked way better than Titan brand) masking tape 4 small binder clips kettle and water a marble optional for tasting water: Q-tips, one per student Procedure Prepare the activity: Lay a piece of cling wrap over the top of the plastic tub. Use masking tape to secure the cling wrap most of the way round, leaving it open the last 1/4 of the length. Add the salt and food colouring at one end of the plastic tub (make separate piles). Place the pot in the middle of the tub. Alternatively, students can later add the salt as you visit each of their tables to set up the water cycle model. In class: Boil the water, then immediately add it on top of the salt to a depth below the rim of the pot (it will not work unless the water is only just boiled). Clip the lid shut by securing the cling wrap with binder clips. The cling wrap may balloon up. Place the marble in the middle of the cling wrap, and push the cling wrap down, so that the marble is directly over the pot. After 5 mins or so, drips of re-condensed water will fall from under the marble into the pot. After 10 or 15 minutes there will be enough drips of water in the pot to have made a puddle. The students can optionally taste the water in the pot ("the lake") and the tray ("ocean") - give them a Q tip to dip first in the lake water and taste, then use the other end of the Q tip to dip in the ocean and taste. The ocean water is salty and the lake water is fresh. Only the water evaporates from the ocean - the salt is left behind. The food colouring also stays in the ocean, but does not appear in the lake. Grades taught Gr 1 Gr 2 Gr 3
