Groundwater · Crystal MineScience for kids

Where does rainwater go when it soaks into the ground?

In short: Some rain seeps down through tiny gaps and cracks in soil and rock and is stored underground as groundwater. It moves slowly, bubbling out at springs or forming pools and streams in caves.

How it works

Soil and many rocks look solid, but they are full of tiny holes and cracks, a bit like a sponge. After rain, some water is taken up by plants or evaporates, while the rest trickles slowly downwards until it fills the gaps below.

A layer of rock or gravel that holds plenty of water is called an aquifer, and the top of the soaked zone is the water table. Groundwater is not usually a giant underground lake; it is water tucked between sand grains and in cracks, moving very slowly.

Where groundwater meets lower ground, it flows out as a spring. In limestone areas, water dissolves passages in the rock, creating cave pools and underground streams. Wells tap groundwater too, which is why keeping the land clean matters: pollution can soak down with the rain.

Where to see it in New Zealand

Te Waikoropupū Springs near Tākaka in Golden Bay are famous for their extraordinarily clear water, which rises from groundwater stored in marble rock. Christchurch's tap water also comes mainly from aquifers beneath the Canterbury Plains.

Try it together

In a clear plastic cup, add a layer of small stones, then sand, then soil. Slowly pour in water and watch through the side as it trickles down and collects at the bottom. That wet bottom layer is like a mini aquifer, and its top is the water table.

Kids also ask

Is groundwater the same as an underground river?

Usually not. Most groundwater sits in tiny spaces between grains and in cracks. Only where rock such as limestone dissolves easily can water carve wide tunnels and form real underground streams.

Can you drink groundwater straight away?

Not always. Some groundwater is filtered clean by rock, but it can also carry germs or pollution from the surface. Well and spring water should be tested or treated, so never drink untreated water outdoors.

In the game, “Groundwater” is a nature card on Crystal Mine.

Your child finds this card by reaching the right place or meeting the right weather on the island, and lights it up by answering the question on the back. Tap the button below and the game shows your child which island it is on and how to find it. Mochi Isle is a browser learning game for ages 5 to 18; the main island and the daily lesson are free.

Find “Groundwater” on the island ↗ All cards from Crystal Mine