They're great because you can use a lot of items from around the house, and it's a good way to re-use those plastic bottles. Some educational stores sell bottles similar to these, and they're expensive! I like this frugal alternative.
I've found that the SOBE lifewater bottles are perfect for this project, as the labels are shrink wrapped, so you don't have the sticky adhesive to contend with.
This time around, we made 3 different bottles. The first is the wave bottle. All you need is baby oil, and tap water. Tint the water with food coloring, and pour half oil, half water in the bottle. Easy, and relaxing to look at :) I added a few teeny plastic fish from my older daughter's Barbie collection, but they're a little hard to see.
The second bottle we made is simply water with a little Mr. Bubble solution, sequins, and glitter. You can tint the water if you like. I left it clear because. . .I just liked it that way.
The last one we made used up some of the colored pasta we had in the craft bin. Then I put a few little plastic figures and animals in for some fun objects to look for. Little girl loves to make noise with this one!
Easy! Just remember to seal the caps tightly! And always supervise your toddler with these. Have fun :)