When exploring the countertop filter reviews with reverse osmosis, many suggestions are about choosing the best countertop reverse osmosis system for filtration.
Are you looking for a good, most efficient, and most innovative countertop drinking water filter?
Which reverse osmosis filter systems will be suitable for investment?
If you are concerned with your water quality and looking for expert advice, you’ve clicked on this good article, which is explained after deep research, testing, and reviewing residential osmosis water filters systems. We observed after deep analysis and testing their features and capabilities. The Countertop reverse osmosis drinking water filters are the best reverse osmosis water system that provides contaminant-free water.
The drinking water contains various contaminants, including lead, arsenic, mercury, pharmaceuticals, hormones, radionuclides, and chemicals. A perfect water filter system cleans the drinking water because a standard carbon-based filter can not filter all harmful contaminants, But RO water filters can remove them nicely.
Countertop RO water filters review
In this article guideline, we would like to share
- Five countertops reverse osmosis filters in 2021
- Compare the RO system with other processes and the most important things you need to consider while selecting countertop water filters.
Top 3 Pick Of Countertop Water Filter Systems
- Brand AQUA TRU
- Capacity 3 Quarts
- Material Plastic
- LxWxH 14 x 12 x 14 inches
- Exclusive 4-Stage
- Ultra RO Technology
- BPA Free
- Brand Waterdrop
- The integrated smart display screen
- 0.0001 micron RO membrane
- The impressive 3:1 drain ratio
- The CF filter and MRO filter can last up to 6 and 18 months respectively
- Brand: APEC Water Systems
- Capacity: 90 Gallons
- Material: Aluminum
- Item Dimensions LxWxH: 15.5 x 6.5 x 6.5 inches
- Item Weight: 10 Pounds
- Purification Method: Activated Carbon, Reverse Osmosis
- Countertop RO water filters review
- Best countertop Reverse Osmosis water filter reviews 2021
- AquaTru Countertop Reverse Osmosis System
- Frizzlife WA99 countertop RO water filter system
- Crystal Quest Portable Countertop Reverse Osmosis System
- Waterdrop Countertop Reverse osmosis Filter System
- APEC RO-CTOP countertop water filter system
- AlcaPure Countertop Reverse Osmosis Water Filter by RKIN
- SimPure Y6 countertop reverse osmosis water filtration
- Buyer’s guide for countertop RO water filter
- Working of countertop reverse osmosis filters
- Consider the things before buying countertop RO water filters
- FREQUENTLY ASKED QUESTIONS
Best countertop Reverse Osmosis water filter reviews 2021
Here are the top 7 best reverse osmosis water filtration systems.
- AquaTru Countertop RO Water Filter system
- Frizzlife-WA99 Countertop Reverse Osmosis Water Filter system
- Crystal Quest Portable Reverse Osmosis water filter
- Waterdrop Countertop Reverse Osmosis Water Filters
- APEC RO-CTOP Countertop Reverse osmosis water filter
- AlcaPure Countertop Reverse Osmosis Water Filter by RKIN
- SimPure Y6 countertop reverse osmosis water filtration system
|AquaTru - Countertop Water Filtration Purification System||Check Price On Amazon|
|Frizzlife WA99 RO Countertop Water Filtration System||Check Price On Frizzlife|
|Crystal Quest Countertop RO Water Filter System||Check Price On Amazon|
|Waterdrop N1 Countertop RO Water Filter System||Check Price On Amazon|
|APEC Water Systems RO-CTOP-C Portable Countertop RO System||Check Price On Amazon|
|AlcaPure RO Countertop Water Filter System||Check Price On Amazon|
|SimPure Y6 Countertop RO Water Filtration System||Check Price On Amazon|
AquaTru Countertop Reverse Osmosis System
The AquaTru Countertop RO water filter system has NSF certification for 42, 53, 58, 401, and p473 to remove 82 different contaminants from drinking water. It removes chromium-6 (97.2%), cyst (99.99%), fluoride (93.5%), lead (99.1%), chlorine (96.6%), Bisphenol A (99.0%), PFOA & PFOS (97.5%), VOCs (most >99%) some pharmaceutics.
Benefits of using AquaTru countertop RO system
- AquaTru countertop drinking water filter provides the best, fairest, purest, and most reliable drinking water.
- AquaTru’s four-stage countertop Reverse Osmosis filters can plug into your electricity and running instantly.
- Installation and plumbing free
- Sleek and modern look
- One year warranty
- The drain ratio is 3:1
- People can refill the tank in 10-15 minutes, and water is directly dispensed by pushing a button
- the indicator indicates the filter replacement
AquaTru recommended Erin Brockovich; the clean water Advocate recommended the Aquatru water purifier system.
The AquaTru has a quality of 4 stage filtration, which removes contaminants including chromium-6, fluoride, dust and sand particles, lead, pesticides, cysts, chlorine, some pharmaceuticals, etc.; it has a pressure pump designated to work faster.
AquaTru stages 1st & 2nd have a coconut shell CR pre-filter, removing dust and rust particles and various chemicals like chlorine.
3rd stage is made up of a reverse osmosis membrane which eliminates heavy metals.
A 4th stage has an activated carbon filter, That removes -15x more contaminants.
The system’s efficiency can be estimated as around 80% clean water and wastes around 20%. Water is dispensed by pressing a button. AquaTru reverse osmosis filters last for approximately 6 to 12 months, almost 600 gallons, and reverse osmotic membrane lasts for two years (1,200 gallons).
- Highly efficient countertop water filters system with reverse osmosis 4-stage filtration
- installation free
- Provide hundreds of gallons per day of purified filtered water
- NSF standard certified
- dripping or leaking problem reviewed by some persons.
- Some people experienced a fault in machines.
It is also considered the best countertop drinking water filter, mainly named Frizzlife WA99 RO Countertop Water Filter, which has a powerful filtration system with a smart display. This RO system removes up to 99% of water pollutants such as chlorine, fluoride, radium, arsenic lead, and mercury.
Benefits of using frizzlife drinking water filter system as a best reverse osmosis water filter
- Frizzlife WA99 reverse osmosis filters have a stylish and modern look.
- It has 0.0001-micron precision.
- It has TDS monitoring.
- One of the best benefits is Its water filtration 5:1 (drain ratio).
- It has a Twist-in placement.
- It is installation-free.
- It is WQA certified.
- Frizzlife installing a system is very easy; you need to plug it into an electric circuit and let it purify your water by the glass.
- It can easily fit on your countertop.
- Frizzlife can be used in the office, bedroom, and any other place.
Frizzlife WA99 reverse osmosis countertop water filter has four filters. Sediment filter traps floating particles like sand, dirt, and silt. Carbon block filter reduces the amount of chlorine and other chemicals. RO membrane filters more than 1,000 different water impurities, importantly lead, arsenic, mercury, radium, parasites, bacteria and viruses, chromium, etc. Granular activated carbon reduces organic compounds in the water and makes a better taste—sediment and carbon block last for six months. US-made Membrane GAC filter lasts for 12 months.
Frizzlife performs circular filtration, which re-filter the water to achieve a 5:1 drain ratio. Recycling of water means re-filtration or multi-filtration reduces the amount of wastewater.
TDS monitoring feature of Frizzlife water purifier is used to get pure water that is 100% pure. TDS stands for Total Dissolved Particles, which tells the exact TDS level of incoming and outgoing water. The outgoing high TDS level indicates the replacement filter. You can easily replace the filter by twisting and clicking with the help of a spanner wrench.
Frizzlife filter was the most preferred choice by the customer is observed. We recommend this system for those who can’t afford the others one.
- Compact and stylish design
- Installation free
- 99% filtration of more than 1,000 contaminants
- Highly accurate smart display and easy to fit
- Excellent water drainage ratio 5:1
- The little water tank needs to refill several times per day
- Warranty not available
Crystal Quest Portable Countertop Reverse Osmosis System
The crystal quest portable RO system is the best portable, more convenient reverse osmosis water filter. It removed the waste product, cysts (cryptosporidium, giardia), sand, rust, dirt other dissolved matter, including heavy metals like lead, nickel, copper, lead, aluminum, cadmium, chromium, and other dissolved metals, by an electrochemical process. They are attached as magnets to the media surface.
Benefits Of Crystal Quest Portable Countertop Reverse Osmosis System
- Like all countertop models, it’s installation-free
- It is compact, stylish, and occupies less space
- It requires little maintenance
- It is more portable than the other options mentioned
- it doesn't require electric power to run
- It is lightweight and fully equipped
- Components are iso certified
- Operation cost is Low
- Combination of filtration GAC, KDF, RO, and multistage
- Water pressure is good, 40 PSI or higher
STAGE 1 remove suspended particles such as silt, sediment, cysts, sand, and dirt.
STAGE 2 removes chlorine (99.9%), chemicals linked to cancer, volatile organic compounds, PCBs, MTBE’s many more.
STAGE 3 reduces other undesirable particles.
STAGE 4 & 5 removes and filters particles such as salts, elements, minerals, most microorganisms, chlorine-resistant cysts like Cryptosporidium, and inorganic substances.
STAGE 6,7 & 8 Water flows through the redox process, which removes many unwanted contaminants from water. Chlorine and hydrogen sulfide are removed. Heavy metals attached like a magnet are eradicated through an electrochemical process and remove the hardness of the water.
STAGE 9 & 10 result in significantly reducing or eliminating various contaminants producing pure and safe water.
- Ten stages of filtration for water purification
- water capacity is 50GPD
- 1-year warranty available
- no installation is required.
- filters with good life-span
- Minimum maintenance is required.
- No NSF certified
- Produces little water for a large family
- It is slower than other countertop RO water filter systems.
Waterdrop Countertop Reverse osmosis Filter System
The Waterdrop Reverse Osmosis water filter systems have a 0.0001-micron membrane to remove 999 TDS and other impurities. It contains Uv purification technology that helps to kill pathogens like bacteria and viruses. It is certified by NSF, WQA, and IAPMO, including removing VOCs, nitrates, heavy elements like mercury, copper, arsenic, fluoride, etc.
Benefits Of Using Waterdrop Countertop Reverse osmosis Filter System
- Maintenance is easy, and no central installation is required
- Smart display screen allows homeowners to monitor the overall water quality closely
- The drain ratio is 3:1and drain water recycling technology reduces the water consumption rate
- The daily production rate is 75G
- The CF filter and MRO filter have a prolonged duration of 6 and 18 months, respectively.
- Its UV feature kills pathogens like viruses and bacteria, making the water safe and pure.
- Offers good performance with removing up to 90% of TDS
- It is the least wasteful system on the list because it only wastes 1 gallon over 3 gallons of water produced
- It contains five-in-one features of the TDS display, a Filter life indicator, multiple volume settings, a Water shortage indicator, and an Auto-flush indicator
Unlike the standard countertop RO systems with more water drainage, the waterdrop countertop offers minor water drainage. It doesn’t have a power consumption issue because the system goes for sleep and stand-by mode automatically.
The waterdrop water filter has three filter stages of powerful filtration
- solid carbon block filter removes chlorine improves odor and taste
- a reverse osmosis membrane removes chemicals, heavy metals, and TDS
- PP cotton removes suspended solids, rust, sand, and other impurities
The three filter stages of the waterdrop water filter consolidate to remove various contaminants, including rust, chlorine, lead, PFAS, nitrates, and fluoride.
The installation process doesn’t require any tool, drilling, plumbing. Just there, insert the plug into the socket, enjoy the filtered water at any place. The filter replacement also doesn’t require any tool.
The filter has Longer Lifespan, which is more reliable. The filters provide their services for 6 to 18 months. Newborn babies are sensitive, so their milk powder with RO filtered water is easily absorbed by them compared to tap water because RO water is suitable for toddlers to Protect each toddler’s health.
- less water wastage
- drain ratio 3:1
- no fixture and installation required
- smart appearance
- dripping issue
APEC RO-CTOP countertop water filter system
APEC RO-CTOP Water Systems is one of the best portable countertop water filters with a 99% removal rate. It removed cadmium, arsenic, barium, chromium, copper, lead, Floride, and many more.
Benefits of using APEC RO-CTOP as the best reverse osmosis water filter
APEC high capacity filter system occupies 4-Stage Filtration technology with prolong services produced in the USA. These high-capacity filters have four stages.
1st stage consists of a 5-micron sediment filter which removes dust, rust and debris, particles and protects the membrane.
2nd stage contains a coconut shell activated carbon filter, which improves the taste, discoloration, and odors, removes chlorine, cloudiness, and Volatile Organic Chemicals from the water to make it healthier, safe ultra-pure drinking water.
3rd stage contains a FILMTEC RO membrane with high salt rejection capability and resistance to bacteria fouling which removes 99% of TDS and contaminants such as arsenic, leads, fluoride, chromium, radium, and many more.
4th stage filtration contains a coconut shell activated CR filter, which removes all the possible residual left behind.
It sets to the Most Standard Faucet because it doesn’t fit particular type designed and sprayer faucets. RO-CTOP-C countertop filter is designed with simple installation and maintenance. It is very reliable for apartments, offices, condominiums, homes, and students to carry.
It has a capacity of 90 gallons of water per day at 60 psi water pressure. For each gallon of water produced, only 2 gallons are wasted. Its wasted rate is lower than other countertop water filter systems, with an average of 3 gallons of wastage.
- Four-stage deep filtration
- Easy to carry, easy to install
- It is one of the best portable systems
- one gallon of purified water produced with two gallons of wastage better than other with average three gallons of wastage rate.
- 1-year warranty available
- ut doesn’t have a tank for water storage.
- It doesn’t fit on all faucets.
- Filters take time for their replacement.
- The flow rate is minimum.
AlcaPure Countertop Reverse Osmosis Water Filter by RKIN
AlcaPure Zero installation countertop water filter’s RO membrane is NSF 58 certified, removing contaminants like nitrate & nitrite, heavy metals like lead, copper, fluoride, and many other pollutants. It is also one of the best filters in osmosis water filtration systems, removing 99% of impurities to access healthy water.
Benefits of using zero installation as the best reverse osmosis water filter
- The most plus point of AlcaPure is that it maintains the pH of water up to 7 to 8
- Reverse osmosis tends to have acidic pH in water, and an alkaline post filter turns its alkaline nature.
- It has an innovative display and a beautiful look with no installation
- It adds calcium and magnesium to the drinking water
- Good drain ratio 1:1
- Utilize less electric power
- The water storage tank is bisphenol-A & S organic compound-free
- Its filters life span is long-lasting with minimum maintenance.
- filters replacement needs 6-12 months, and RO membrane lasts for two to three years
- Take 15-20 minutes for the water refilling.
Zero installation countertop is the best reverse osmosis water filter with the fashionable and latest design, which even enhances the beauty of the kitchen. Zero installation is a secured method that converts concentrated or contaminated water into fresh, filtered water with an alkaline taste.
It has deep filtration with four stages which eliminate all the harmful pollutants.
Stage 1 consists of a Five-Micron Sediment Filter with two layers, an inner and an outer layer. The inner layer traps small size particles, and the outer layer captures large size particles. The dirt and debris are removed here.
Stage 2 is made of coconut activated carbon filter, which excludes cancer-causing agents like trihalomethanes, improves the odor and volatile organic chemicals.
Stage 3 consists of a semipermeable RO Membrane, a paramount central core that produces 75 gallons of water in a reverse osmosis system.
Stage 4 comprises AlcaPure post-filter, which remineralizes the essential minerals known as calcium and magnesium for their alkaline pH.
Filter capacity is outstanding; the indicator indicates the replacement of filter with minimum effort. Filters provide its services for one year, and RO membrane serves for 2-3 years.
- 1-year money-back guarantee and 1-year warranty available
- Long-lasting and high capacity filters
- 1 gallon of the purified filter with 1 gallon of wastage rate
- Reminerlizer adds calcium and magnesium to the water to make it tasteful.
- Consume power less than a bulb.
- malfunctioning noted by the costumers
SimPure Y6 countertop reverse osmosis water filtration
SimPure countertop reverse osmosis water filtration has 0.0001 microns membrane to remove 99.99% of the 1,000+ contaminants, PFOA/PFOS, Pharmaceuticals, heavy metals like Arsenic, Lead, chlorine, TDS fluoride, nitrites & nitrates, etc. The simpure countertop ro filter uses UV sterilization technology to remove 99% of the drinking water bacteria, viruses, and germs.
Benefits Of Using SimPure Y6 countertop reverse osmosis water filtration
- Having a smart look and compact design
- Installation is not required
- It has UV purifying technology for sterilization
- Simpure water purifier has efficiency; it has the lowest drain ratio of 5:1
- It has high water dispensing flow rate
- Pour 250ml water in 15 seconds
- You can take it with you anywhere with its power equipment
- One of the best features of simpure y6 is its hot eclectic cattle which provide hot water
SimPure y6 UV technology with reverse osmosis filter system has 3-stages of filtration.
Stage 1 and 2 contain PP+CTO Filter, which removes dust, rust, sediments, organic substances, pesticides, chlorine, and other radioactive substances. It also improves water taste and smell.
Stage 3 contains a 0.000-micron RO filter membrane, which eradicates microorganisms, salt, organic waste, heavy elements, and other harmful substances.
The life span of the composite PP+CTO filter and RO filter is 6-12 months, and an Indicator is present on its apparatus to represent the need for a replacement filter.
The installation doesn’t require any tool; it just needs a socket where its plug is inserted. Just to push the button and have a purified and safe water. No efforts are required for the installation and replacement of filters. Like other Under-Sink water Filtration systems, SimPure Y6 doesn’t occupy more space; you can take it everywhere kitchen, office, bedroom, Outdoor, etc., with its electrical supply.
It has different ranges of temperature to provide hot water and purified water.
- 198F or 92C for tea lovers
- 185F or 85C for coffee lovers
- 113 or F45C for warm water or milk
Simpure y6 purifying reverse osmosis system provides 250ml in just 15 seconds and 1 Liter water in 1 minute. Its re-filtration ability makes water neat and clean and reduces wastage, and saves up to 1500%. So no think more it’s best household purifier system to meet water needs with saving money.
- The drain ratio is 5:1
- Flow rate is 418 Gallon Per Day
- Free from BPA
- Certified from NSF
- Removes 99.9% of contaminants
- Fairly a large system
- Malfunctioning issue
Buyer’s guide for countertop RO water filter
What is a countertop reverse osmosis filter?
Reverse osmosis or RO is a phenomenon of filtration in which water is forced to pass through tiny pores of a semi-permeable membrane to eradicate contaminants, including bacteria, heavy metals, and produce highly purified. Carbon-based filters will remove chlorine, and other chemicals from water bur RO filters remove all contaminants filtering them to a much higher level. The RO semi-permeable membrane contains tiny pores that only water molecules can pass through and left others as a residue.
Working of countertop reverse osmosis filters
RO countertop water filters provide water in two ways; one directly from a faucet and a tank for filling. When water is injected into the water system, it crosses stages of filtration to give pure, safe, and ultra-pure water. Its general stages of filtrations can explain the working of the countertop.
- As the name indicates, water runs through a sediment filter, removing dust, rust, and debris.
- A granular carbon filter or activated carbon filter is the next filter that follows adsorption, removes chlorine, volatile organic compounds (VOCs), chemicals, improves taste and odor from drinking water.
- The reverse osmosis membrane excludes 99.9% of TDS from the water.
- A second carbon filter or a post-filter removes any lingering sediment.
- Some countertop reverse osmosis systems with remineralization filters add calcium and magnesium for balancing pH.
Advantages of countertop drinking water filter
- They have a hassle-free installation easily manageable for renters or homeowners.
- They don’t require alteration of plumbing systems.
- They require minimal maintenance.
- They are typically compact, lightweight, and portable.
- The countertop drinking water filter removes up to 99% of TDS.
- It provides clean, taste-free, and smell-free water.
- Most countertop Reverse Osmosis systems are installed under the kitchen sink.
- The filtration speed of countertop RO water filters is usually very perfect.
- These are perfect for traveling, so you can take them with you to any place anywhere.
- Countertop water filters deliver water directly don’t have tanks for storage.
- Countertop Reverse osmosis filter systems are considered the best water filters for getting contaminant-free water.
Disadvantages of countertop drinking water filter
No doubt, the countertop water filter is the most effective method available in the market today. As it prevents particles from entering your water, but it has few disadvantages also.
- The countertop water filter waste more water.
- According to the EPA, “Reverse osmosis filters use almost three times as much as water as they treat. It may affect your bills. Some household reverse osmosis systems only recover water from 5%-15% of the filtered water.
- Pressure drop is reported in many countertop water filters.
- Wastewater is disposed
- The reverse osmosis system is not suitable for toddlers due to lacking minerals.
Consider the things before buying countertop RO water filters
These are the following qualities that a person should consider for investing in a countertop water filter.
Water Pressure and flow rate
If the Greater the water pressure, the greater will be flow or speed rate. More substantial water pressure will increase water flow which will immediately pass through the semipermeable membrane. The greater the water pressure, the lower will be the wastage rate. Less flow rate increases water wastage.
Water pressure isn’t crucial for an electric system because the current induces speed in the flowing of water.
Production or wastage of water by the filter
Production and wastage of water is a significant thing to consider while selecting your water filter. More wastage of water will affect your bills. Every filter produces water, and some have more wastage, and some have a little wastage rate. So it’s the nature of the countertop reverse osmosis filter that when water is produced, water is wasted too. When the water passes through the Reverse Osmosis membrane, every single contaminant can’t pass through it. During the Reverse Osmosis process, these contaminants settle down and drain naturally by wastage of water.
Let suppose; You will invest in a water filter that fulfills the requirements of gallons per day. That’s why GPD is very important to check to invest in a filter. For families, good GDP value ranges from 50 GDP to 90 GDP depending upon families. If you love planting and gardening, then you may go for higher rates.
Remineralization of water
Many countertop water filters are available in the market, like the aquasana countertop water filter, which effectively removes contaminants with its remineralization ability. It’s not a reverse osmosis technique but add minerals to the water to make it healthy. Similarly, reverse osmosis technology removes minerals from the water that is not good enough, so we should go for the best countertop RO filters that remineralize the water to make it healthful.
Some RO water filters with remineralizing strength give essential minerals to your drinking water to get alkaline. It is a good option who want mineral water taste or prefer health interests.
Storage tank Capacity
Storage tank capacity would be the consideration for people who buy filters without faucet connections. These filters have a water storage tank, and water is refilled after usage.
Some Reverse Osmosis filters don’t have a tank for storage. They provide water directly.
The water source with contaminants
When you search for countertop reverse osmosis filters, the water source with contaminants is an important thing to consider.
In general, Reverse Osmosis countertop filters removes a variety of chemicals, heavy metals, and pollutants. According to the research, reverse osmosis countertop water filter fails to filter substances like fungicides, pesticides, herbicides, and water dissolved gases.
Filter Life Service
It is not convenient to change water filters again and again. So it would help if you considered the filters having lifespan services from 6 months for pre and post-filters to 2 years for RO membranes.
Filter replacement is a very crucial point to be aware of with its replacement. Otherwise, you will not be able to get purified water.
Counter Space Availability & Installation
Consider the counter space available for their settlement. Go for the countertop reverse osmosis systems with smaller footprints, compact and intelligent designs that don’t occupy more space.
Installation should be easy and convenient for renters and homeowners. The countertop Reverse Osmosis water filter systems install without taking extra time. Some don’t even need assembling; they need a socket and plug to start.
Filters certification for removal of contaminants
Certification word provides peace to your mind and gives satisfaction for the usage of products. Consider your countertop reverse osmosis systems with certification. NSF systems certified for 58 and 372 for removal of various contaminants and disposal of lead components, NSF 42 for chlorine, 53 for lead removal. NSF-certified products mean products with the approval of a third party.
Maintenance of Reverse Osmosis water filter systems
The countertop reverse osmosis water filter systems are comfortable to maintain and are accessible rather than other filters.
- Change the filters on time.
- Clean the dust and rust timely from a soft cloth so they no dirt deposit on it.
So here are the best reviews for the countertop water filter systems that may help access clean and pure water to drink. They are convenient investments rather than the daily purchasing of gallons. They are very reliable to take them everywhere easily with little or no effort. Reverse osmosis systems remove 99% of the contaminants from the water. Even for small to large family reverse osmosis systems are portable and provide enough water to meet their requirements.
FREQUENTLY ASKED QUESTIONS
Some others question’s answers for our readers that might be helpful for reading.
How much water is produced by the reverse osmosis system?
The countertop water filters produce 45 to 340 liters per day under the water pressure of 40 to 100psi.
Is it suitable to drink water from reverse osmosis water filters every time?
No, reverse osmosis water is not suitable to drink all the time because it contains fewer minerals content. According to WHO, less mineral uptake is not appropriate to consume and can negatively affect health.
Why is reverse osmosis water dangerous sometimes?
Reverse osmosis water is not free from harmful contaminants but also removes out healthy minerals, which can cause the water acidic, and continuous drinking acidic water can cause gastric and kidney problems.