Cat litters - Which one to Choose?

3 Interesting Facts about Cat Litter:
1.  Businessman and entrepreneur Ed Lowe invented and trademarked Kitty Litter® in 1948 as the first commercially marketed cat litter. In that time the most popular litter pan materials were sand and fireplace ashes.
2. Cat waste can contain a nasty parasite called Toxoplasma which can cause some serious health problems to humans. Wastewater treatment systems are primarily designed to handle human waste and aren’t designed to handle things like Toxoplasma. Unfortunately, wastewater treatment systems don’t remove this parasite from the water before it is discharged back into the environment. The harm can also extend into waterways and marine ecosystems affecting fish, shellfish, otters, and other marine life  
3.  To avoid being eaten or attacked by predators, ancestral cats had to cover up their tracks. The smarter cats gravitated toward soft dirt or sand, since their granular consistency made it easier to bury their waste. This is why cats are naturally attracted to the feel of cat litter and know what to do once they feel it beneath their paws.

3 Recommended Qualities for cat litter?

1. Grain Size.  In litter preference studies, cats consistently and significantly favor litter made of very small granular (sand-like) material over large granule litter made with other types of substrates.
2. Non-Scented.  Many cats are averse to odor control additives and may also have an aversion to litters with a floral or citrus scent. The chemical fragrances in many cat litters can also be toxic to cats.
3. Dust free​ Many mass market cat litters contain significant amounts of silica dust which has been linked to upper respiratory issues in cats and even humans. 

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3 of the main cat litters we have experienced - Pros & Cons

Crystal Cat litter
Crystal Cat litter is made up of Silica gel which is composed of silica dioxide sand, oxygen and water. The gel is made up of tiny pores that absorb 40 times their weight in liquid. Most of us recognize silica gel as those little “dessicant—do not eat” packets that come with medications, cameras, shoes and other items that could be damaged by moisture buildup. 
Pros

• High absorption of urine and efficient odor control
•  Bacteria are less likely to grow in the crystal litter than in other types of litter because it does not contain sugar or carbohydrate
• less frequent litter box changes 

Cons

• One of the most potentially serious is the chance that your cat, or more likely, your kitten may eat some of the crystals. If your cat eats litter crystals, he/she could face some life-threatening medical situations.

• There is a tendency for urine to pool in the litter box when the crystals become saturated.  Although manufacturers recommend daily stirring of the crystals.

• Large rough shape of the crystals may irritate little paws.

• More expensive?  May be offset by the fact that you need to replace it less often

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Biodegradable Litters 
In the US it is considered that there are nearly 75 million cats and up to 150,000 tons of cat litter that end up in landfills every year. For this reason alone it may be worth considering biodegradable cat litter as an option for your cat.  
Biodegradable litters come in different forms: wheat, corn, walnut and paper.
The ones most often seen through our Barcelona pet sitting experience are the clumping and non clumping corn varieties.

Pros

• Biodegradable, supports the environment
• Many of them have no added chemicals
• Some are dust free
• odor control is good

Cons

• Because many biodegradable litters are based on plant material (they contain carbohydrate and sugar), care should be taken with storage to prevent insect infestations and to prevent the growth of mold, and the aflatoxins. 
• They can be messy
• Some are not dust free
• some may cause allergies

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Clay litter
Clay litter is composed of absorbent, diverse clay minerals called "fuller's earth." Fuller's earth is any non-plastic clay or clay material that can be used to filter, decolorize and absorb liquids and spills. It has been popular for decades and has the innate ability to absorb its own weight in water. 
Pros:
It will effectively absorb moisture as well as provide some odor control through absorption.

• There are many alternative uses for clay litter, including motor oil clean-up, soaking up "barbeque run off" and traction for icy driveways.
• It is also relatively inexpensive compared to other products on the market. 

Cons of clay litter:

• While clay litter effectively absorbs moisture, if the soiled litter isn't replaced often enough, the urine will collect at the bottom of the box. The bacteria in the urine will multiply and convert the uric acid into foul-smelling ammonia.
• It is dusty and can cause respiratory problems in both cats and humans.
• It is obtained through strip mining, which has a negative impact on the environment. 
• It does not break down naturally - leaving landfills full of soiled cat litter.

Clumping or Scoopable Cat litter
Clumping litter is also a clay-based litter, but the main ingredient, sodium bentonite, acts as a clumping agent, absorbing urine and turning it into tight, solid clumps that can be easily removed from the litter box and disposed of. 
Pros:

• “Urine clumps” eliminate odor build-up and keep the box cleaner.
• It is virtually dust free.
• Ideal for mechanical or sifting litter boxes.
• It works well with multi-cat households.

Cons:

• There has been much debate about the safety of clumping litter in regard to a cat ingesting the litter and becoming ill. It has been suggested (but not clinically proven) that if ingested – the clumping litter will expand in the cat’s intestinal track and absorb moisture in the cat’s body, creating intestinal blockages and dehydration. As such, many clumping litter products are not recommended for kittens – who often times play in litter pans and ingest litter.
• Do NOT flush! Due to the highly absorbent nature of clumping litter, flushing it down the toilet can cause it to expand and damage plumbing.
• Green hazard: Clumping litter is also collected from strip mining and is NOT biodegradable.
• It's more expensive than regular clay litter.

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3 things to help you to choose a scoop
As pet sitters, scooping litter efficiently is all about the right scoop!

1. Size of holes in your scoop need to match the cat litter type.
2. Have two scoops especially for the non clumping clay litter types. They are not expensive. One that has holes to match the granule size and another that does not have holes to scoop up urine from the bottom of the tray.
3. Keep it simple but good quality.​

Conclusion

• In my research i found it very useful to read the reviews on the various litters.
• Your cat will also naturally gravitate to the litter it prefers.
• Considering the population of cats as pets, it is wise to choose an 'environmentally friendly' cat litter.
• Do not flush litters down the toilet due to the toxiplasmosis risk to groundwaters and the marine environment. Cat waste may also block up sewerage systems.
• It is all about the scoop. Choose the right scoop for your litter.
• It is always advisable to remove the urine waste from a cat litter tray to maintain maximum sanitation.
• Dust free seems to be the healthiest choice.
  

References
www.petsit.com/pick-of-the-litter​
https://www.huffpost.com/entry/
www.vetinfo.com/pros-cons-crystal-cat-litter.html
www.moneycrashers.com/best-natural-cat-litter-reviews/
https://www.consumersearch.com/cat-litter/best-biodegradable-cat-litter
https://flohawks.com/do-not-flush-cat-poop-down-your-toilet/
https://www.litter-robot.com/blog/2015/06/30/why-do-cats-use-litter-boxes/