Under Sink Water Purifier Disadvantages: An Honest List

The main disadvantages of an under sink water purifier are that it needs free cabinet space and plumbing access, a hole in the counter for its faucet, a drain connection for reject water, and a higher upfront cost than basic wall units. A badly installed one can also leak unseen inside the cabinet. Most of these are solved by good installation, but if your cabinet is full or you rent without permission to drill, a wall-mounted purifier is the better choice.

The Disadvantages at a Glance

Disadvantage	How much it matters	Mitigation
Uses cabinet space	High in small kitchens	Measure first; plan storage around it
Needs plumbing access	Medium	Professional installation; check inlet and drain positions
Counter hole for the faucet	Medium; permanent	Drill once, in the right place; some sinks have a spare hole
Harder to reach for service	Low to medium	Keep the cabinet front clear; rely on monitoring alerts
Renters may need permission	High for tenants	Ask the owner first, or choose wall-mounted
Reject-water drain line	Low (all RO needs a drain)	Route it properly to the sink waste
Higher upfront cost	Medium	Compare five-year costs, not just sticker price
Leak risk inside a cabinet	Low if well installed; serious if not	Quality fittings, a leak check, regular look under the sink

For the full picture of how under sink RO works and what to look for, see our under sink RO water purifier buying guide. Below, each disadvantage in detail.

Cabinet Space and Plumbing

Space. The purifier and its storage tank take up most of the cabinet under the sink, which in many Indian kitchens is already home to the waste pipe, a dustbin and cleaning supplies. In a compact kitchen this is the biggest real cost of going under sink. Open the cabinet and measure before you buy: width, depth and height, minus the space the waste pipe and any sink basket take.

Plumbing. The purifier needs an inlet from the cold water line and a drain connection, both inside the cabinet. In most modern kitchens these are close by. In older kitchens or unusual layouts, the installer may need to extend a line. This is a one-time job, but it is why under sink purifiers are not a casual DIY install. Our water purifier installation guide explains what a proper installation involves.

Power. An RO purifier needs electricity, so you need a socket inside or near the cabinet. If there is none, add one before installation day.

The Faucet Hole and Harder Access

The faucet hole. An under sink purifier dispenses through its own faucet on the counter or sink deck. That usually means drilling a hole in the countertop. On granite or quartz this is routine for a trained installer, but it is permanent. Some sinks come with a spare tap hole that can be used instead. Decide on the faucet position carefully: within easy reach, clear of the main tap, and over the sink.

Harder access. Filters and the tank sit in a cabinet, so service means kneeling and clearing the cabinet. For most owners this matters little, because filter changes and servicing happen only occasionally and are done by a technician. It matters more for anyone who likes to do their own maintenance or who has difficulty bending down. A purifier with monitoring that alerts you on filter health removes the need to keep checking inside the cabinet.

Renting, the Drain Line and Upfront Cost

Renting. Drilling a countertop and changing plumbing are changes to the owner’s property. Tenants should ask permission in writing first. If the answer is no, or you move often, a wall-mounted purifier needs only a few wall fixings and is easier to take with you.

The drain line. All RO purifiers, under sink or wall-mounted, send some reject water to a drain. Under sink, the drain line connects into the sink waste inside the cabinet, which is actually tidy. The disadvantage is only that it must be routed properly, without kinks and with the right fitting, or it can gurgle or drip.

Upfront cost. Under sink purifiers usually cost more than basic wall-mounted units, partly for the faucet and fittings and partly because of the more involved installation. Look at the five-year cost instead of the sticker price: filters, service and any maintenance plan often decide the true difference.

Leak Risk Inside a Cabinet

This is the disadvantage worth taking most seriously. A wall-mounted purifier that drips is visible immediately. An under sink purifier that drips may go unnoticed for days, soaking the cabinet floor. Wooden and particle-board cabinets swell when they stay wet.

Leaks almost always come from installation, not from the purifier itself: a fitting not fully seated, a pipe cut unevenly, a drain connection pushed rather than secured. Mitigation is straightforward:

• Use installation by trained technicians rather than a general plumber unfamiliar with RO fittings.
• Ask the installer to run the purifier and check every joint before leaving.
• Look under the sink after the first day and the first week, then whenever you open the cabinet.
• Keep the cabinet floor clear enough that you would see water.

Who Should Not Buy Under Sink

• Tenants without written permission to drill the counter or alter plumbing.
• Kitchens where the under sink cabinet is small or already full.
• People who move house often.
• Anyone who wants to see the display and dispense at a glance at standing height.
• Buyers whose budget is tight, where a basic wall unit does the same purification job.

For these homes, a wall-mounted RO is the practical answer. Boon Homie is a wall-mounted RO with a 5-stage UltraOsmosis process, in-line LED UV before the tank, a 20 litres per hour rate into an 8-litre tank and WaterAI monitoring, ₹21,900 at the time of writing. If you are still weighing formats, our under sink vs countertop comparison sets out the trade-offs side by side.

Who Should, and Where Boon Tap Fits

Under sink suits owners renovating or setting up a kitchen, households who want a clear counter and wall, and modular kitchens with a spare cabinet and a power point nearby. If you have the space and can drill the counter, its disadvantages are mostly handled at installation.

Boon Tap is an under sink RO: the purifier sits in the cabinet below the counter with a dedicated faucet on the counter. It has an 8-stage UltraOsmosis RO rated for input up to 2000 TDS, an 8-litre tank and WaterAI monitoring, so filter health is visible without opening the cabinet. Installation is free and done by Boon’s own team, not a third-party agency, which is the main answer to the leak and plumbing concerns above. It carries a 2-year warranty and a 10-day money-back guarantee, and is from ₹23,500 at the time of writing. If your TDS is low, Boon Tap UF, which has no RO, exists for those supplies.

Frequently Asked Questions

What are the disadvantages of an under sink water purifier?

It takes up cabinet space, needs plumbing and power access under the sink, requires a hole in the counter for its faucet, needs a drain connection for reject water, usually costs more upfront than a basic wall unit, and a badly installed one can leak unseen inside the cabinet. Most of these are handled by careful measurement and professional installation.

Do under sink water purifiers leak?

A well-installed under sink purifier should not leak. Leaks almost always come from installation: a fitting not fully seated, an uneven pipe cut or a poorly secured drain connection. Because the unit is in a cabinet, a drip can go unnoticed. Use trained installers, ask them to check every joint, and look under the sink after the first day and week.

Can I install an under sink water purifier in a rented flat?

Only with the owner’s permission, ideally in writing, because it usually means drilling a hole in the countertop and connecting to the plumbing. If the owner says no, or you move often, a wall-mounted purifier is more practical. It needs only a few wall fixings, a water point, a drain and power, and is easier to take with you.

Does an under sink RO need a hole in the countertop?

Usually, yes. The purifier dispenses through its own faucet, which is mounted through a hole in the countertop or sink deck. On granite or quartz a trained installer can drill it cleanly, but it is permanent. Some sinks have a spare tap hole that can be used instead, so check yours before installation day and agree the faucet position in advance.

Is an under sink water purifier harder to service?

Slightly. The filters and tank sit inside the cabinet, so a technician has to clear the cabinet and work at floor level. For most owners this makes little difference, because filter changes and servicing are occasional and done by the brand’s technician. A purifier that shows filter health and alerts you removes the need to check inside the cabinet yourself.

Who should choose wall-mounted instead of under sink?

Choose wall-mounted if you rent without permission to drill, your under sink cabinet is small or full, you move house often, you want the display at standing height, or your budget is tight. A wall-mounted RO gives the same kind of purification without a counter hole or cabinet space, and is simpler to install and reach.