What if the pond starts to lose water?

If the UK’s privatised water companies with their multi-million pound budgets suffer from the consequences of leaks and are frustrated by how difficult they are to locate then many pond keepers who have also suffered from the same problem (less the large budget!) can sympathise that leaks can also be a frustrating distraction from the main thrust of koi keeping.

However, if upon suspecting a leak, rather than going to the extremes of emptying a pond and examining every square inch with the stealth of Sherlock Holmes, it would be wise, as any fine detective would agree, to think laterally and look for alternative causes other than the obvious.

Reasons for a drop in water level other than a leaking pond.

1. Leaking pipework.

Where filters are external to the pond and above the water level, tiny hairline splits in hose or perished washers in hose unions can all be common causes of losing water.

If possible inspect the soil along the run of the pipe and at best inspect all hoses and pipework at first hand. Try to isolate leaking pipes from the other possible causes of a dropping water level by running the pond without the filter over night to see if this has any adverse effect on the water level.

2. Bog areas and sunken rockwork.

Submerged marginal planted areas or partially submerged rock work can act as blotting paper, drawing water out of the pond and into the surrounding soil, cement or lawned area. These problems usually manifest themselves just after a pond has been constructed when such a phenomenon has not yet been accepted as a ‘characteristic’ of that pond. The rate of ‘blotting’ will also increase with temperature, being at its most extreme in the summer months. There is little that can be done to prevent water rising by capillary action but it is useful to be able to associate such a drop in water level with capillary action rather than a leak.

3. Splash-out

When viewed for a few minutes, the odd drop of water splashing onto a patio from a fountain, bamboo heron scarer, or escaping from the spray bar of a filter may seem insignificant . Yet such a ‘drip….drip….’ can soon add up to a loss of several gallons causing the water level to drop. It is vital to try to avoid any splash-out even if it means adjusting or choosing a less adventurous fountain head. This is even more important in a self-contained water feature where the reservoir is much less limited than in a pond.

4. Waterfalls

When constructing a pond, waterfalls can be one of the most difficult features to perfect. Not only must they complement the character and size of the pond, they also have to be watertight. The most straightforward way of ensuring that all of the water that feeds a waterfall runs into the pond is to build the waterfall and pond from the same piece of liner. In this way, if the stepped rockwork of a waterfall were to settle, crack and spring a leak then any leaking water will still return into the pond if only out of sight and under the construction.

If such preventative action is not carried out then water loss from a waterfall can be infuriating leading to quite extensive and costly remedial work. In addition, any prolonged leakage from a waterfall (or a pond) can cause subsidence problems which may manifest themselves as structural weaknesses in the future.

5. Evaporation

Rates of water loss from a pond through evaporation can be quite significant, especially where water is passed through fountains or over waterfalls. Of course, evaporation rates are greatest in warmer weather which should be taken into account when trying to discount it as a possible cause for losing water. To be able to eliminate evaporation as a cause of water loss is difficult but if the pond is mature and such water loss has not been encountered before, it will usually point to your worst fears – a leak!


Probably the biggest headache about discovering a pond has a leak is discovering where the leak is.

Other questions that may arise during a leak are:

Is there only one hole? If I find it, how do I mend it? If I do find it and mend it, will another hole take its place in a few weeks? If I have to empty the pond to fix it, where do I put all of the koi? What caused the leak and is it likely to happen again?

Finding a leak.

Having eliminated all of the other possible causes of water loss and being confident with your own judgement that the leak is occurring within the pond, the simplest way of locating the leak (or at least the deepest leak) is to let gravity and water take their course and see where the dropping water level finally rests. Where the tide stops marks the level where the pond perimeter will have to be inspected. The ease with which you can locate a hole depends on the extent of any algal growth and how close the tide mark is to the pond surface for ease of inspection. However, the greatest factor affecting the ease with which a hole may be found is the material with which the pond is made. This also determines how the hole(s) once located may be repaired.

Liner (PVC/Butyl)

The smooth nature of a liner means that a hole should be relatively easy to find, but care must be taken to examine under folds and creases. Close inspection of the liner should also give you an idea as to the condition of the liner as a whole (some may become brittle with age) and allow you to decide whether it is worth mending, or whether a new liner ( with a lengthy lifetime guarantee) may be the better option. A repair will either involve a patch/glue affair or the use of a strip of pliable adhesive tape. Either way it is vital that the liner surface is thoroughly cleaned and dried prior to applying the patch.


Holes in a concrete pond can be very difficult to locate as the porous nature of the material concerned can mask even the smallest of holes. More often than not a reapplication of waterproofing sealant or re-render is required. Either way it is likely to involve putting you pond into ‘dry dock’ and finding your fish some temporary, quality alternative accommodation (often a tough task in itself).

Fibreglass Coated Blockwork

Locating holes in this can be just as difficult as finding them in concrete, depending on the quality and thickness of the resin used in its finishing top coat. A reapplication of resin may solve the leak, but requires excellent preparation of the old surface and as with concrete, will more than likely mean draining the pond completely.

Pre-formed Fibreglass Ponds

Leaks are a very rare occurrence, and only usually occur through very poor installation of a freak and brutal accident with a garden fork. If not too large, these can be repaired using a resin based repair kit.

Worst Nightmare.

If having left the pond water to find its own level and you find it eventually empties completely (or down to the water table) I’m afraid you have encountered a pondkeepers (and water company’s) worst nightmare; a subterranean leak beneath the pond floor either at the bottom drain or associated pipework. It does happen, especially after years of settlement, and it is a problem that does not bear thinking about!

Prevention is better than cure.

Leaks can spell hours of heartache and even lead to the loss of a well balanced pond system, even perhaps to a full strip-down. There are specific causes of leaks that are out of our control, such a heron damage, natural life of the material and accidents with garden implements.

However, if using a liner (which is the most common pond making material), by treating pond construction with forward planning, and removing stones and tree roots and using underlay or sand prior to laying a liner. It can be tempting to treat such a well manufactured material a little roughly at times which will only increase the likelihood of leaks in the future. Yet if installed correctly, there is no reason why a pond liner should not still be with you intact well past its lengthy guarantee.

Kill blanketweed and string algae.