Water

The gravitational pull of the Moon and the Sun attracts ocean water — causing it to rise regularly (high tide) and fall (low tide). The Moon is closer to Earth — so its effect is the greatest. During full moon and new moon, the gravitational forces of both the Moon and the Sun combine — producing the largest tides (spring tides).

Spring tides — occur when the Sun, Moon, and Earth are in a straight line (full moon/new moon): the gravitational forces of both combine — producing the largest tides. Neap tides — occur when the Sun and Moon are at 90° to each other: the forces partially cancel each other out — producing smaller tides.

Ocean currents are large, continuous flows of water within the ocean that follow fixed paths. Warm current: Gulf Stream (keeps Europe warm). Cold current: Labrador Current (brings cold conditions along the coast of Canada). These currents regulate the world's climate.

The Gulf Stream is a warm current — it flows from the Gulf of Mexico to the coast of Europe. Because of this, Europe's ports remain open throughout the year and the region experiences milder winters — whereas Canada, at the same latitude, is much colder due to the Labrador Cold Current.

(1) Evaporation — the Sun turns water into water vapour; (2) Condensation — the vapour cools and forms clouds; (3) Precipitation — rain or snow falls; (4) Collection — water returns to rivers, oceans, and the ground. Then it begins again — this cycle never stops.

(1) Turn off the tap — while brushing teeth or using soap (an open tap wastes 16 litres per minute); (2) Rainwater harvesting — collect rooftop rainwater in the ground or in a tank; (3) Drip irrigation — deliver water directly to the roots of plants. Also: repair leaks, and reuse water from air conditioners and RO purifiers.