For preformed waterfalls - plastic and fibreglass

Check around the lips of the individual units and make sure there is no water travelling back to the soil along the edges.

Check there is no water overflowing over the back of the unit. This is a particular problem with very flexible, plastic waterfall sections. As the soil beneath consolidates or an ingress of rainwater below the units washes away the sand bed the units rest on, the support for the units is undermined and they tip and crumple. As they do this, the problem is exacerbated as water spills out, undermining the units even more.

CURES:- Many of the mass produced waterfall and stream units are not finished as well as they might be. The rush and turmoil of the production line sometimes results in the odd unit not being cut precisely right from the raw material. This is no real problem since there is generally too much material left on the shape rather than too much cut away.

1. Check the inlet pipe at the head of the streams. Backward drips can be a problem.

2. Check that the water is not flowing from the units properly because they are badly positioned or that they have moved.

If they have moved, nestle them back into their beds with more support from the back. Not only can sand can be washed away easily soil can sink or be eroded by ants. Well-placed rocks lend more dependable support.

Try to gain some more permanent support from a foundation of stone and nestle the unit in a bed of semi-dry cement and sand or mortar mix. Make sure that there are strategic barriers of rock and stone to prevent the new bed from washing into the pool before it has 'gone off'.

3. If the water still runs backwards towards the rockery despite repositioning then it is time to get out the knife or hack saw. Cut away a bit at a time along the bottom edge until the water flows forward.

N.B. When using a sharp knife, like a Stanley knife, always cut away from you.

4. If you still cannot find the fault, check the hose from pump to inlet. Some bright spark might have put a fork or spade through it. But in all my years of water gardening I have only known this happen once and it was me that did it.