You suspect a leak. A copper pipe in the loft has sprung a pinhole leak on the down side of the stopcock. Eltham Plumbers can fix leaks.Tools and materials:Copper slip coupling-15 mmAdjustable spannersPipe cutterOld clothsTorch.Method:1). Going to the kitchen, pull the plug out of the kitchen sink and turn the cold water tap on.2). Turn off the stopcock in the cupboard under the sink.3). Wait a few minutes for the cold water tap to stop running, and then go up into the loft and press down on the floating ball valve in the cold water storage tank. If it stays silent, with no water running out, you can be certain that the leaking pipe has been drained.4). Centre to the slip coupling on the pinhole leak and use a couple of tabs of sticky tape to mark the pipe so that you know whereabouts the coupling needs to be fitted.5). If the pipe is hardly dented at the leak, take your pipe cutter and cut through the plight, right through the pinhole. If, on the other hand, the pipe is badly dented at the pinhole, use a cutter to take out a ring sized piece of pipe that includes the pinhole.6). Use a cloth to dry and clean the two ends of the pipe.7). Ease the two pipe ends apart. Disassemble the slip coupling and slide a cap nut, followed by an olive, on each pipe end. An Eltham Plumber can do this.8). Slide the body of the slip coupling on one pipe end, then ease the pipes back together and slide the coupling back so that both ends are contained and the body of the coupling is centred on the leak.9). With your fingers, screw the cap nuts as tight as possible, and then use the adjustable spanner to clench up the joints. Do not over tighten, no more than about 1 1/4 turns. Wipe the coupling with tissue.10). Go down into the kitchen at the stopcock on. When the cold water tap starts to run, turn it off. Go back to the loft and inspect the repaired joint. Allowing for a small amount of condensation on the pipe, if the area stays dry, you have fixed the leak.