That line of water outside the shower door is easy to misread as a much bigger problem. The bath mat is damp, there is a thin shiny trail across the tiles, and it can start to look as if the glass has been fitted badly, the floor has the wrong fall, or the bathroom waterproofing is beginning to fail. Quite often, though, the issue is much smaller: the seal along the bottom edge of the door is not holding the water back.
Sometimes the seal is simply worn. The edge has gone stiff, curled, or yellowed. Sometimes it is more awkward than that: you have already replaced it once, but the new one is the wrong shape, thickness, or direction for the door. The water still finds the same route out, gets wiped away, and comes back the next time someone showers.
Before you start thinking about replacing the whole screen, crouch down and look at the bottom edge of the door. Check whether the water is coming from under the glass or travelling round from the side. Look at whether the seal is actually gripping the glass, and whether that small deflector lip is facing the direction where it needs to hold water back. Often, the first money-saving step is not buying something larger. It is working out whether the smallest part has been chosen correctly.
Before Calling It a Bathroom Leak, Find Where the Water Starts
Next time before using the shower, try one simple check. Dry the tiles outside the door and move the bath mat out of the way, so it does not absorb the water before you can see what is happening. Shower as normal, with the door closed. There is no need to aim the water deliberately at the gap or wipe the floor straight away. Just watch for where the first line of water appears during normal use.
The small puddle outside the door is the easiest thing to misread. Water follows the fall of the tiles, and a bath mat can drag moisture into a wider patch, so the wettest area is not always where the leak began. Stand to the side of the door for a moment and watch whether the water is slowly appearing from the middle of the bottom edge, or whether it starts near a corner and then runs along the base.
If it is hard to see, a piece of kitchen roll is more reliable than guessing. Hold it near the bottom of the door, then near the side edge, then near the wall-side corner. Within a few seconds, you will usually see which area becomes damp first. If the paper gets wet at the middle of the bottom edge, the issue is more likely to be at the base of the door. If the side becomes wet first, the line of water along the bottom may simply be where it travelled afterwards. It can also help to look again a minute or two after showering, as some water does not drip straight away but slowly works its way down the glass.
At this point, you are not shopping. You are simply working out the route the water is taking. Where it starts tells you which part to check next.
If Water Comes from the Bottom Edge, Check Whether the Seal Is Loose, Too Short, or Facing the Wrong Way
Once you know the water is coming from the bottom of the door, look closely at the line where the seal meets the glass. It is worth looking beyond whether the seal has fallen off. Check whether the channel gripping the glass is loose, whether there is a gap near the floor or threshold, and whether the deflector edge is carrying water back into the shower area.
Some bottom seals still look as if they are in place, but the grip has loosened. Push the strip gently from side to side. If the whole piece slides on the glass, or one section can be lifted easily, water may be getting between the glass and the seal. The drop can also be wrong. If the soft fin is too short, a narrow gap is left under the door when it is closed. If it is too long, it can be pushed up by the threshold and curl back after a few uses.
The direction of the deflector is easy to miss. Most bottom seals have a small angled lip or soft fin. Fitted correctly, it uses the flow of water to guide it back into the shower area. Fitted the wrong way round, the water can hit the fin instead, and a fine line of moisture will still appear outside the door. So the question is not simply whether the seal is new, but whether that soft fin is sitting where the water actually passes.
A more useful next step is to work out whether the seal is failing because it is loose, cannot reach the gap, or is directing water the wrong way. From there, it is easier to compare the structure of 
The Old Strip Is a Clue, Not a Template
A lot of wrong purchases happen because the old seal is treated as the answer. Once it has been removed, its shape may already have been changed by limescale, door movement, and years of pressure. In some cases, the old strip was never the right style in the first place, especially if the shower has leaked ever since it was fitted.
Start with the glass thickness. Most bottom seals grip directly onto the glass, so if this measurement is wrong, every other judgement becomes less reliable. If the channel is too loose, the seal can slowly slip after a few showers. If it is too tight, it may be difficult to fit, or it may not press onto the glass properly at all. Use a ruler on the glass edge rather than guessing by eye. If there is limescale on the edge, clean it first so the measurement is clearer.
Next, measure the distance between the bottom of the door and the threshold, floor, or water bar beneath it. This tells you how much drop the seal needs. Close the door in its normal position and look at the gap below it. Do not only measure the middle; check both ends as well. A door that has dropped slightly may have an uneven gap along the bottom. If one end has a noticeably larger space, replacing the seal with the same drop all the way along may help the centre but leave the corner exposed.
The profile is the part people often skip. Once the old strip is off, look at it from the side. Is it a straight strip, or does it have an angled deflector? Is it a single soft lip, or does it have a firmer guide edge? A close photo helps, especially if you are comparing products online. Take the strip from the front, from the side, and in position on the glass if you can. Many seals look similar when they are lying flat on a table; the real difference is often the angle of the deflector, the length of the soft fin, or whether it sits in the right place once fitted.
If the Bottom Seal Looks Right, Check the Corners and Side Connections
If the shape, thickness and drop all seem right, it is worth pausing before ordering the same part again. The bottom seal deals with water travelling out from the base of the door, but it is not the only barrier on the screen. Sometimes the water is not escaping from the middle at all. It is working its way out at one of the lower corners, or at the point where the bottom seal meets the vertical seal.
Start with the two ends of the door. If the middle stays dry after a shower but a short line of water appears near the lower left or lower right corner, the issue may be at the end rather than along the whole strip. The bottom seal may not reach the side properly, or there may be a small gap where it meets the edge of the door. That gap can be only a few millimetres, but water will still follow the glass and find its way out.
Then look at the point where the bottom seal meets the vertical seal. Many shower doors do not rely on one piece of seal to do everything. The bottom, side, and magnetic edges each deal with water from different directions. The bottom seal blocks water from below; the vertical seal deals with the side gap. If the two do not meet cleanly, water can slip through that small break. Close the door, hold a dry piece of kitchen roll near the lower corner, and let the water run normally on the inside of the door. If the paper gets damp there first, the corner is worth checking more closely.
If the leak is concentrated at the corner, the answer may be to adjust the end position of the bottom seal, check whether the vertical seal is sitting properly, or add a short water bar in the right place. The aim is not to keep adding parts. It is to make sure the side, lower corner, and bottom edge form one continuous route that water cannot easily pass through.
Describe the Leak Clearly Before Guessing Again
With this kind of bathroom problem, slowing the checking process down is often the useful part. After a shower, take a photo of where the water appeared before mopping it away. When you remove the old seal, keep it for a moment and take a picture of how it sat on the glass. Before comparing replacements, put the glass thickness, bottom gap, and profile shape into a note on your phone. It is much easier than trying to remember those details while looking at product images later.
If you are not sure what type of seal you have, describe the problem more specifically. Is the water coming from the middle of the bottom edge or from the lower left corner? Is the seal sliding, curling, or loose at the grip? When the door is closed, is there a gap along the whole bottom edge, or only at one end? This is where a specialist site can be easier than a general marketplace. SIMBA Seals, for example, groups the seals on showerdoorseal.uk by bottom, side, magnetic and curved styles, so the question becomes more precise: not “the bathroom is leaking”, but “the water starts at the bottom edge, the glass is this thick, and the old profile looks like this”.
Many people are not unwilling to fix the problem. They are simply starting from the same puddle each time and guessing again: is it the bottom, the side, or the whole door? One person replaces the seal and still finds water at the corner. Another assumes the bottom is leaking, only to realise the side was getting wet first. Sometimes, one glass measurement would have saved a second order.
The next time you see that line of water outside the shower door, you will at least know where to look first, instead of wiping it away and starting the same guesswork again.
