How to Install an RO Water Purifier at Home: Step-by-Step Guide with Diagrams

Before You Start: What You Need

Most households in Bangladesh can install a standard under-sink or countertop RO purifier in 1–2 hours with no specialist plumbing skills. Before starting, confirm you have:

Tools required:

• Adjustable wrench or spanner
• Drill with masonry bit (for wall mounting)
• Screwdriver (Phillips and flat)
• Teflon (PTFE) tape for thread sealing
• Bucket and towels for any water spillage

Connections required at your installation site:

• A cold water supply line (municipal tap or borehole pump — must be cold water only, never hot)
• A drain connection for reject water
• A power outlet nearby for the UV lamp and/or pump
• Under-sink space or countertop space for the unit and tank

Water pressure check: RO purifiers require a minimum inlet pressure of 30–40 PSI (2–2.8 bar) to function. Low-pressure situations (top-floor flats, intermittent supply) may require a booster pump. Fill a bucket from your tap and time it — 10 litres in under 60 seconds indicates adequate pressure.

Step 1 — Choose Your Installation Location

Under-sink (most common): The purifier unit mounts inside the cabinet under your kitchen sink. The storage tank sits alongside it. The dedicated faucet installs through the sink deck or the countertop. This is the neatest installation — all components hidden.

Countertop/wall-mount: The unit mounts on the wall above or beside the sink with a tube feeding from the tap inlet and a separate tube draining to the sink. Requires no drilling into the sink deck.

Choose a location that keeps the purifier protected from direct sunlight (UV degrades plastic tubing) and within reach of a power outlet.

Step 2 — Install the Dedicated Faucet

For under-sink installations, the purified water faucet needs its own hole in the sink or countertop.

1. Select the position for your faucet — typically alongside your existing tap
2. Drill through the sink deck or countertop using the appropriate drill bit (masonry bit for stone/ceramic, hole saw for stainless steel sinks)
3. Pass the faucet stem through the hole from above
4. Secure from underneath with the provided nut and washer
5. Attach the supply tube from the purifier tank to the faucet stem — these typically use push-fit connections (push tube in firmly until it clicks and seats)

Common mistake: Not tightening the faucet base firmly enough. It will loosen over time with use and eventually spin. Tighten firmly, then check again.

Step 3 — Connect the Cold Water Feed Line

Your purifier connects to your existing cold water supply line using a feed water adaptor (also called a saddle valve or T-connector — included with most purifiers).

1. Turn off the water supply to your kitchen (close the isolation valve under the sink or turn off the main supply)
2. Open the kitchen tap to release remaining water pressure in the line
3. Attach the saddle valve to the cold water supply pipe — it clamps around the existing pipe. Do not use this on the hot water line.
4. Wrap 2–3 layers of Teflon tape around all male threads before connecting — this prevents slow drips that become problems over time
5. Connect the feed water tube (usually blue or clear, 1/4 inch diameter) from the saddle valve to the inlet port on your sediment pre-filter housing

Important: The tube connections use push-fit fittings. Push firmly and straight until you feel the tube bottom out. Tug gently to confirm it is seated — it should not pull out easily.

Step 4 — Connect the Drain Line

The reject water from your RO membrane drains continuously while the purifier is making water. It must connect to your kitchen drain pipe.

1. Attach the drain saddle clamp to your drain pipe — typically the white or grey PVC pipe under the sink
2. Drill through the drain pipe using the included bit (the clamp has a guide hole)
3. Connect the reject water tube (usually black or red, 3/8 inch diameter) to the drain saddle
4. Ensure the drain tube has a slight downward slope from the purifier to the drain connection — water must flow by gravity

Common mistake: The drain tube is kinked or runs upward at any point. Reject water must drain freely — any obstruction causes back-pressure that forces contaminated water back through the system.

Step 5 — Connect the Storage Tank

The pressurised storage tank stores purified water ready for immediate dispensing.

1. Wrap Teflon tape around the tank valve thread
2. Screw the tank ball valve (included) firmly onto the tank
3. Connect the tank tube from the purifier housing to the ball valve — again using push-fit connections
4. Leave the ball valve in the open position (handle parallel to the tube)

Check your tank pressure before first use. A new tank should be pre-charged to 7–8 PSI. Use a standard tyre pressure gauge on the Schrader valve (like a bicycle tyre valve) at the bottom of the tank.

Step 6 — Connect the UV Lamp and Power

If your purifier includes a UV stage:

1. Connect the UV lamp module inline after the membrane and before the post-carbon filter — the exact connection point is marked in your installation diagram
2. Plug the UV lamp transformer into a nearby power outlet
3. The UV lamp should illuminate immediately when powered — you may see a faint blue-purple glow through any transparent housing sections

Step 7 — First Flush and System Check

Before drinking any water, the system must be flushed:

1. Turn on the water supply to the purifier
2. Open the purified water faucet at the sink
3. Let the system run and drain for the first full tank capacity (7–10 litres) — this flushes manufacturing residue and carbon fines from the new filters
4. Close the faucet and let the second tank fill (approximately 2–3 hours)
5. Flush the second tank completely as well

After two full flushes, test your purified water with a TDS meter. Compare against your source water TDS — you should see 90–97% reduction. If you see less than 85% reduction, check all tube connections for correct seating and verify the membrane is installed in the correct orientation (there is a feed side and a permeate side marked on the membrane housing).

Common Installation Mistakes to Avoid

Verifying Your Installation Is Working

After installation and flushing, confirm these three things before using the system for drinking water:

1. TDS reading — purified water TDS should be 90–97% lower than source water
2. No visible drips — inspect all connections and the drain saddle 30 minutes after first use
3. UV lamp — confirm the lamp indicator light is on and the lamp has power

Write today's date on each filter with a permanent marker — this is your maintenance reference point for the replacement schedule.