Hong Kong's subtropical climate douses its citizens with an average 2,214mm of rain each year. Most of it falls in summer, making life sticky and uncomfortable at times. And as if dealing with humidity in the home was not enough of a challenge, you're in deeper trouble if water is getting in. Dampness and interiors simply don't mix. Quite apart from damaging your furnishings and looking ugly on your walls, the mould and fungal growth that dampness gives rise to can be unhealthy. Mould pollutes the indoor air, producing allergens that can cause allergic reactions, irritants and, in some cases, potentially toxic substances. There are unseen nasties as well, such as dust mites and viruses, which thrive in damp, warm conditions. One 2007 American study has even drawn a link to mental health, suggesting that people who live in damp, mouldy surroundings are at increased risk of depression. Any water that enters a building can also compromise its structure, affecting its value when it's time to sell. Would you buy a property, or even sign a lease if there is obvious water damage? With the rainy season upon us, and the heavens opening, it's time to take remedial action. The first step is to ascertain where the water is coming from. Ian Sabransky, waterproofing consultant with Astel (Advance Specialist Treatment Engineering Limited) Hong Kong, says there are three major areas of concern: rising damp from beneath a floor slab, leaking roofs and leaky window or door frames. Of these, probably the most troublesome is rising damp and, unfortunately, there is no quick fix. The best course of action is to remove the tiles or floor finishes and cover the entire slab with a waterproof membrane. However, a localised solution is sometimes possible, says Sabransky. This involves lifting the floor tiles or finishes in a specific area, identifying the weak points and injecting polyurethane or acrylic resins into cracks in the concrete. The problem, he says, is that water has a way of getting in - if you stop it in one spot it might find another. 'You could be chasing your tail.' It's also possible to put a clear polyurethane or similar type of coating over the tiles, but this is prone to failure in the long run, or may turn a milky colour. Sabransky says it's more suitable for bathrooms where water may be splashed from a shower, rather than a solution to rising damp where water is pushed up under pressure. The only reliable solution for a damp floor is to bite the bullet and pull it up, he says. With leaky windows and doors, gaps must be properly sealed - usually that will mean removing the existing frame and recaulking around it. If wind-driven water is seeping in from the walls, it could mean that your building is porous - a common problem with concrete village houses and not always visible on the outside. External walls can be coated with decorative elastic waterproof coatings to stop this leakage. Another common problem is a leaky roof - most likely the culprit will be drainage, or lack thereof. Again, the first step is to identify the source and if it's a drain malfunction, fix it. Sabransky says it is also 'quite straightforward' to cover the rooftop with a waterproof membrane. 'Liquid membranes ideally should be applied to the structural roof slab, so roof finishes must be removed. The cheaper types are bitumen-based or cementitious membranes. The more expensive ones are MMA [methyl methacrylate], polyurethane or polyurea membranes. It is possible to keep the roof finishes and place a UV stable trafficable sheet membrane such as reinforced TPO [thermoplastic polyolefin].' With any waterproofing solution, Sabransky says the devil is in the detail. 'The success of any waterproofing membrane is how well the details are done at terminations, penetrations and rainwater outlets. Proper care at any construction joints and movement joints will pay off in the long term. Good surface preparation of substrates to receive waterproofing is critical to the success of the work,' says Sabransky, who gives advice to architects, building owners and infrastructure developers in Hong Kong and around the region. What will it cost? Sabransky says waterproof membrane products can cost from HK$50 to HK$200 a square metre. 'It is beneficial to do the refurbishment against leakage or rising damp only once and get it right. For peace of mind and to get economy into the repairs there must be time taken to do proper planning and investigation before a decision is made on what to do to fix your problem. The cheapest quotations are not always the answer.' Apart from leaks, there are other ways water can get into your home. Condensation in a non-air-conditioned space is created when there is a temperature difference of more than 5 degrees Celsius. So if hot, humid air comes in contact with a cool surface, like air on an icy-cold beer glass, condensation will form on the cool surface. Hence the trick is to keep the temperature in an indoor environment relatively constant. The team at Indoor Air Quality Solutions Centre, run by the Business Environment Council ( www.bec.org.hk ), offers the following tips to minimise moisture content: Ventilate when you can. Open windows at night during the cooler months, but when the evening temperature creeps above 25 degrees Celcius then it's time for the air conditioner. Homes in heavily vegetated areas typically suffer more from mould. Put clothes away dry because storing damp clothing is likely to promote mould growth. Avoid having very hot showers, which create steam and spread condensation - just a few degrees drop in water temperature can make a difference. An extractor fan also helps to reduce condensation. When cooking, put lids on pots to save energy and reduce steam and condensation. A good extractor over hobs also removes excess moisture. Ceiling fans also help evaporate water and dry the indoor environment. Going on holiday? Use timer switches on ACs with drying function to help keep the internal humidity down and create some air flow. An hour a day may help keep the mould away. Clean AC filters regularly. Ensure potted plants don't get infested with mould and spread spores. Open up cupboards and leave them open occasionally to improve air flow. Use anti-mould, but environmentally friendly, paints to reduce mould growth. Despite every best effort you will still need to run dehumidifiers in our climate and the market is flooded with choice. The Electrical and Mechanical Services Department (EMSD) has a downloadable brochure on its website, helping you choose appliances on the basis of energy efficiency. Choosing an appliance with an EMSD Energy Label will save 10 per cent of your electricity costs per year, it claims. For a room of about 200 sq ft, EMSD recommends a 5-litre model to avoid having to run the appliance flat out. A dehumidifier with automatic control is also recommended to maintain a specific humidity and save energy. It is advisable to keep dehumidifiers away from corners and clean them regularly, including the dust filter. Don't obstruct the air intake and outlet to allow sufficient heat dissipation. Keep windows and doors closed and place the appliance away from direct sunlight or heated equipment. The Indoor Air Quality Solutions Centre says the only fair basis for comparing home dehumidifiers is to look at energy consumption/litres of water removed from the air. 'Understanding that the goal is to reduce excess humidity is also important - we are not trying to create a desert. Setting the level too low uses too much energy,' says a spokesman.