Bath Time Science: Water Experiments for Young Children

Bath time is already a science lab. Water pours, objects float and sink, bubbles form and pop. With a few small changes you can turn ordinary splashing into questions and experiments.

The one rule: never leave a young child alone in or near water, even for a moment. If you need to fetch something, take the child with you, or gather everything before you start. Keep the water shallow and comfortably warm to your wrist, not hot. Anyone caring for a child at bath time, whether a parent or carer, a grandparent or a nanny, should stay within arm’s reach.

Use ordinary bath products sparingly, and do not use anything that is not meant for skin. Nothing here is to be drunk or tasted.

What you need

Plastic cups, a jug, a sponge, a spoon, a plastic bottle with small holes, a few toys, a flannel and some items from the kitchen like a plastic spoon or a clean yoghurt pot. Everything should be too large to swallow.

1. Sink or float

Gather six things: a plastic cup, a sponge, a spoon, a toy boat, a rubber duck and a clean stone too big to swallow. Ask your child to guess before dropping each one in. Sort them into two piles on the side of the bath.

A good follow-up: push the floating cup under the water and let go. What does it do? Push upward means the water is pushing back. That is a real force, even if the child only says “it pops up”.

2. Make a sinking thing float

Take a lump of play dough or modelling clay. It sinks as a ball. Ask your child to shape it so it floats, perhaps like a boat. When it spreads out into a wide shape, it pushes aside more water and floats. Count how many coins or small plastic counters it can carry before it sinks. Our lesson Why does ice float? uses similar thinking for older children.

3. Pouring and measuring

Give two cups of different sizes. Ask: “How many small cups will fill the big one?” Let them pour, spill and try again. Predict first. You are working on volume, and the early maths that goes with it. For older children, add a measuring jug marked in millilitres.

4. Rain from a sponge

Soak a sponge, hold it above the water and squeeze. Say it is raining. Hold it higher and lower. Then poke holes in the bottom of a clean plastic bottle or yoghurt pot, fill it and watch the streams. An adult should make the holes before bath time. Ask: “What happens if we cover one hole with a finger?” You can talk about how water falls down, always.

5. Bubbles and air

Turn a cup upside down and push it straight down into the water. The water does not fill it, because the cup holds air. Tilt it slowly and watch bubbles escape. Compare with pushing a cup in sideways. Children enjoy discovering that air is something, even though it is invisible. Blowing bubbles through a straw into the water is fun, but supervise so the child does not suck water in.

6. Colour ice cubes

Before bath time, freeze water with a drop of food colouring in an ice cube tray. In the bath, drop in a cube and watch the colour swirl out as it melts. Ask whether it melts faster in warm water or in a cup of cool water. You could try two cups side by side. Use food colouring that is meant for food and avoid staining by rinsing.

What to say

“What do you think will happen?”
“What did you notice?”
“Is it heavy or light? Is it big or small?”
“Can you make it do something different?”

Short sentences and plenty of waiting are enough. You are not teaching vocabulary tests, you are building a feeling that questions about water are interesting.

Ending the bath

Drain the water with the child out of the bath. Dry all toys, as damp toys can grow mould. Wipe the bottle or pot and keep a bag for bath science things so you can find them next time.

Where to go next

The post on why a pencil looks broken in water is a lovely next step for children aged six or older. For rainy days, see rainy day science experiments, and the parents page explains how our lessons are organised for families.