We travel around a lot and I am always looking for bits and pieces to keep the children quiet in the back of the car. This Water Magic book was on sale on Amazon last year for £2 so I picked up one for my son. Currently these are selling on Amazon for around £6.78. It is recommended for 36 months plus, due to the pen pieces, however I see no reason why a well super-vised and sensible 2 year old should not be able to use it.
The ringbound 'book' has 6 plain white pages, which are coated with some sort of clever chemical. When they come in contact with water the white disappears and the colour underneath is revealed. The scenes underneath are all farmyard based with plenty of detail, lots of animals to find. Some of the things are outlined on the white coating already so you don't have to search the page blindly, but can choose to start colouring the horse or scarecrow etc first.
The book comes with a pen which rests in a little piece of cardboard attached to the book. You simple remove the reservoir and fill it with water (any old water will do) before reattaching. Where the nib would be on an ordinary pen is a small shaped piece of foam which becomes wet from the water in the reservoir. It is prevented from drying out by a lid. Usually a reservoir of water lasts several weeks if it is only used occasionally, but in the car on a long journey we might have to refill it twice. The pages take a little longer to dry out and return to normal (ten minutes or so), so we have a cloth in the car to help speed the process up a little bit.
There are two negatives to this pen system. Firstly there is no way of holding the pen into the plastic holder, so everytime the book is lifted or moved the pen falls out. This means that the pen is easily lost which can be frustrating for everyone involved. A clip attachment would have been much more useful. Secondly the edges of the pen around the foam are plastic and the nib itself is conical. When my children are using it, sometimes the cone slips and the plastic edge removes some of the white coating over the picture. Some of the pictures which are particularly popular e.g. the tractor on the last page have had almost all of the coating removed and we have only owned it for three or four months.
The water inside is also a source of infinite interest to my children and have occasionally had to remove the pen from a mouth (usually the six year old's mouth!) or other orifice when they have been experimenting. The pages themselves are hard to clean if they have been picked up by a grubby or sticky hand, the coating is very fragile and scrubbing is not a very good idea. Even the occasional gentle application of a baby wipe seems to have thinned the white coating out.
Having said that it is fun and it does keep my children quiet for a while in the car. However it is clear that it is a poor substitute for the permanence and imagination of a felt-tipped pen and some paper, which will be chosen first every time. This is an interesting novelty but not one which captures imagination for very long at all. Both children will pick it up occasionally, have a quick play and then put it down again. Play is even more occasional when the pen is missing, which it usually is, having rolled underneath some piece of furniture. I am pleased with it for the £2 that I paid but I'm not sure I would be happy paying more than £5, unless I had another in the series which the children had responded to.
If farm animals aren't your thing you can also get the Animal version which looks like it features elephants etc. That version also looks like it has a different sort of pen as well, one that is less likely to damage the surface of the picture.